Carlos Alcaraz has lost three matches at the US Open in his career, to Félix Auger-Aliassime, Daniil Medvedev and Botic van de Zandschulp, per his tournament record, and Van de Zandschulp is the only one of the three still in the 2026 draw. The prediction market for his quarterfinal against top seed Alexander Zverev on Wednesday, September 9, is the quietest one on Kalshi's men's board. As of September 8, 2026, at 6:03 a.m. ET, Zverev is 87¢ bid, 88¢ ask. Van de Zandschulp is 12¢ bid, 13¢ ask. Fewer than 7,300 contracts have traded across both legs in the six hours since the market listed, and Tuesday's Shelton-Alcaraz market has traded 45 times that. Read as probability, the No. 1 seed is an 87 to 88 percent favorite over the world No. 70. At a sportsbook that is a line in the -700 range before either side's margin. The question a reader who remembers August 2024 will ask is whether 12 to 13 cents is too cheap for a man who has already done the hardest thing this tournament asks.
My read, before the evidence: the number is not about the Alcaraz match at all, and the reason the crowd has left it alone is sitting on the order book in six-figure size. There is a second wrinkle on Kalshi's tournament board that says what Wednesday is actually worth to each man, and it is not the same number for both of them. Both are below.
The Quick Answer: Kalshi makes Zverev an 87 to 88 percent favorite and Van de Zandschulp a 12 to 13 percent underdog, and the price has not moved because 35,000 contracts of the Dutchman are offered at the ask and more than 146,000 within two cents of it. The full tape, the fee arithmetic on a 13-cent buy, and what the title board says Wednesday is worth to each man are below.
How Zverev And Van De Zandschulp Got To Wednesday
Zverev spent 11 hours and 52 minutes on court through three rounds, most of it in two five-setters, and 2 hours and 30 minutes on Monday. Van de Zandschulp spent 5 hours and 13 minutes on court on Monday alone. That is the shape of Wednesday, and the price already knows it.
The top seed's road, per The Sports Encounter's round-by-round: five sets against Lorenzo Sonego, five more against Quentin Halys in 4 hours and 33 minutes, then straight sets over No. 25 Alejandro Tabilo and a 6-2, 6-2, 7-6(3) win over No. 21 Luciano Darderi on Monday night. Tennis Majors noted after the Halys match that no No. 1 seed in the Open Era had been taken to five sets in each of his first two rounds at a Grand Slam. He is the top seed because Jannik Sinner withdrew with a right knee injury before the draw, which moved Zverev to No. 1, Alcaraz to No. 2 and the two of them to opposite halves. He arrives as this year's French Open champion and Wimbledon finalist, and as the only man to reach the quarterfinals at all four majors in 2026, per Free Malaysia Today's match report. This is his fifth US Open quarterfinal after 2020, 2021, 2023 and 2024, and the 2020 run ended in a final he lost to Dominic Thiem from two sets up.
The Darderi match is the freshest tape and it reads two ways. Zverev landed 72 percent of first serves, won 86 percent of the points behind them, hit 13 aces and won 108 points to 78. He also converted four of 17 break points. "It's a skill to win ugly when you're not playing great tennis," he said after it, and ABC has his other line from the night: "I think after 10 hours on court, I just maybe found my rhythm."
Van de Zandschulp's road, from the same outlet's match report and ABC's: Jan Choinski in the first round, a 6-4, 7-5, 6-2 upset of No. 6 seed Alex de Minaur that was his first win over the Australian in five tries, five sets against Zizou Bergs, and then Monday. Against Arthur Gea, the 21-year-old French lucky loser who got into the draw when Casper Ruud withdrew with a back injury, Van de Zandschulp lost the first set 6-3, lost the second-set tiebreak 7-0, faced match point in the third-set tiebreak, and won 3-6, 6-7(0), 7-6(7), 7-6(3), 6-4. ABC calls it the fourth-longest match in US Open history. He hit 15 aces against nine double faults, and he won 201 points to Gea's 208, which is the kind of scoreline you can only produce by winning the two tiebreaks that mattered and the fifth set that did not need one. "I think this is probably better than the first quarterfinal I made here," he said afterward.
Two players arriving in different shapes, then: the favorite who found his serve after, in his own words, 10 hours, and the underdog who has now played five-setters in back-to-back rounds and has a full day and two nights to recover from the second. A price of 12 to 13 cents seems to have looked at the calendar and the rankings and stopped there. The reason people are asking whether it should have looked further is a single match from two summers ago.
The Alcaraz Match Is Why The Question Exists
On August 29, 2024, Van de Zandschulp, then ranked 74th, beat Alcaraz 6-1, 7-5, 6-4 in the second round on these courts in 2 hours and 19 minutes. The ATP's match report has him winning 28 of 35 points at the net against the World No. 3 and defending champion, whose second-round exit was his first at a major since Wimbledon 2021. He lost to Jack Draper in the next round, and that is worth holding onto: the Alcaraz win did not turn into a run.
The run had already happened, in 2021. Van de Zandschulp came through qualifying that year, beat Carlos Taberner, Casper Ruud, Facundo Bagnis and Diego Schwartzman on the way to the quarterfinals, and became only the third male qualifier ever to get that far at the US Open before Daniil Medvedev, the eventual champion, beat him 6-3, 6-0, 4-6, 7-5. Since then he has beaten Rafael Nadal in the 2024 Davis Cup Finals and Novak Djokovic at Indian Wells in 2025, and he reached a career-high ranking of No. 22 in August 2022. He is 30 now, ranked 70th, and this is his second US Open quarterfinal and second Grand Slam quarterfinal. Zverev, per Tennis Temple, described the US Open as maybe his opponent's favorite tournament, which is the polite way of saying what the record says.
What the record does not contain is a match between these two. The ATP head-to-head is 0-0; Wednesday is their first tour-level meeting, as The Tribune notes. So the price cannot be leaning on a head-to-head the way the Pegula-Navarro number on the women's side leans on a 4-0 record. It is leaning on something else, and the tape shows what.
What Kalshi Is Actually Pricing
On Kalshi, each man is his own yes-or-no contract under the event ticker KXATPMATCH-26SEP09ZVEVAN, paying $1.00 if he wins the quarterfinal and nothing if he does not, with the price in cents standing in for probability, and under Kalshi's rules a retirement after the first ball counts as a win for the man who advances, while a walkover or withdrawal before it is settled at a fair price rather than paid out, and a rain delay just leaves the market open until the rescheduled match ends. If price-as-probability is new, how prediction markets work covers it in plain English and the guide to betting sports on Kalshi walks through orders.
The market listed at 12:05 a.m. ET Tuesday, once both quarterfinal spots were settled, and the first half hour is a lesson in what an empty book looks like. The first Zverev print, at 12:13 a.m., went through at 88¢. Two minutes later someone sold 24 contracts of him at 60¢. At 12:24 a.m. a buyer took 192 contracts of Zverev at 81¢ across three fills in two seconds, and on the other leg a 3-contract print of Van de Zandschulp went through at 62¢ at 12:29 a.m. None of those were prices; they were the first people in a room with nobody on the other side. By 12:40 a.m. a 400-contract buy of Van de Zandschulp at 13¢ had set the level, and it has barely left it since. Between 2:02 and 2:08 a.m. the Zverev leg's three biggest fills of the night, 205, 463 and 1,503 contracts, all went through at 87¢. Every Zverev trade after 2:10 a.m. printed at 88¢. The biggest fill on the Van de Zandschulp side, 1,370 contracts, went through at 13¢ at 3:37 a.m., and every trade on that leg after 2:10 a.m. printed at 12¢ or 13¢.
The one-sidedness is the story. Of the 3,445 contracts traded on the Zverev leg, 3,416 were buyers lifting the offer, 99 percent, at a volume-weighted average of 86.5¢. Of the 3,831 traded on the Van de Zandschulp leg, 3,811 were buyers, 99.5 percent, at an average of 13.1¢. Both crowds have been buying, both have been small, and neither has moved the price.
With the tape in hand, here is the board as it stood at 6:03 a.m. ET Tuesday, with the other three men's quarterfinals beside it for scale.
| Match (Kalshi Event) | Contract | Bid | Ask | Last | Contracts traded | Open interest |
|---|---|---|---|---|---|---|
| Zverev Vs Van De Zandschulp (Wed.) | Alexander Zverev wins | 87¢ | 88¢ | 88¢ | 3,445 | 3,441 |
| Zverev Vs Van De Zandschulp (Wed.) | Botic Van de Zandschulp wins | 12¢ | 13¢ | 13¢ | 3,831 | 3,831 |
| Khachanov Vs Blockx (Wed.) | Karen Khachanov wins | 58¢ | 59¢ | 16,446 | 16,381 | |
| Khachanov Vs Blockx (Wed.) | Alexander Blockx wins | 41¢ | 42¢ | 6,454 | 5,611 | |
| Tiafoe Vs Michelsen (Tue., Not Before 1 P.m. ET) | Frances Tiafoe wins | 57¢ | 58¢ | 266,480 | 208,814 | |
| Tiafoe Vs Michelsen (Tue., Not Before 1 P.m. ET) | Alex Michelsen wins | 42¢ | 43¢ | 88,866 | 86,084 | |
| Shelton Vs Alcaraz (Tue. Night) | Ben Shelton wins | 21¢ | 22¢ | 147,557 | 136,819 | |
| Shelton Vs Alcaraz (Tue. Night) | Carlos Alcaraz wins | 78¢ | 79¢ | 182,488 | 163,344 |
Bid and ask are the live quotes on each yes contract as of September 8, 2026, at 6:03 a.m. ET; contracts traded and open interest are lifetime for each leg, all from one pull of Kalshi's public market data. Wednesday's court and session assignments had not been posted at pull time; the USTA releases the order of play the evening before.
The row worth staring at is not either Zverev row. It is the gap between the two Wednesday matches and the two Tuesday ones. Zverev-Van de Zandschulp has 7,276 contracts across both legs; Tiafoe-Michelsen has 355,347 and Shelton-Alcaraz 330,045. Part of that is time, since the Tuesday markets listed a day earlier, but Khachanov-Blockx listed only two hours before Zverev's market and has already traded three times as much. A quarterfinal with the top seed in it is the one nobody wants to trade, and the reason is that there is nothing to trade about. The price arrived at 87 and 13 in the first hour and every buyer since has paid it.
The Order Book Is The Answer
A price that sits still at 13¢ through 3,800 contracts of one-way buying has a wall behind it, and Kalshi publishes the wall. At 6:03 a.m. ET the resting offers on the Van de Zandschulp leg read 35,319 contracts at 13¢, then 61,071 at 14¢, then 50,376 at 15¢. That is 146,766 contracts of Van de Zandschulp for sale within two cents of the current ask, 38 times what the contract has traded in its life. The bid side is deep too, though not as deep: 720 contracts at 12¢, 24,382 at 11¢, 37,144 at 10¢. On the Zverev leg the picture is the same wall seen from the other side: 2,043 contracts offered at 88¢, 43,042 at 89¢ and 57,206 at 90¢, against bids of 14,816 at 87¢, 40,506 at 86¢ and 34,303 at 85¢. Clearing the 13¢ offer alone takes 35,319 contracts, nine times the leg's lifetime volume, and it only moves the ask to 14¢.
Whoever is offering Van de Zandschulp at 13, 14 and 15 cents in that size is the answer to the question in the title, and the symmetry of the ladders on both legs says it is a market maker quoting both sides rather than one trader with a view. Nobody is arguing the Alcaraz match with them, because the quotes are not pricing the Alcaraz match. They are pricing a No. 1 seed who won 86 percent of his first-serve points on Monday against a No. 70 who was on court for 5 hours and 13 minutes on Monday, and they have priced that view at scale. The crowd that came to buy Van de Zandschulp at 13¢ got filled, all 3,811 contracts of it, and the offer did not thin.
What the wall means: every contract of Van de Zandschulp ever traded could be bought again nine times over at the current ask without moving it a cent. That is a maker willing to sell this price all day, and it tells you nobody with size disagrees enough to lift it.
The sportsbooks had not posted this quarterfinal on OddsShopper's tennis screen at pull time, so the conversion runs from Kalshi's side of the ledger. The underdog's ask converts to 7.7 in decimal odds, a shade under 7-to-1, and his bid to 8.3. The favorite's two quotes convert to 1.15 and 1.14. A book that opens Zverev anywhere in that band is quoting the same probability Kalshi is, before either side's cut, and the worked example below is what the cut does to it.
A Worked Example: What 13¢ Buys
With the exchange's cut included: 100 Van de Zandschulp contracts at 13¢ cost $13 and pay $100 if he wins Wednesday, and Kalshi's published taker fee, 0.07 times contracts times price times one minus price, rounded up to the next cent, takes $0.80 on that order, 6.2 percent of the stake. The same 100 contracts of Zverev at 88¢ cost $88 to win $12, with a $0.74 fee, 0.8 percent of the stake. The fee is small in dollars on the underdog and large as a share of what he risks, so a reader who thinks Van de Zandschulp's true chance is 14 percent is buying a cent of edge before the fee and giving most of it back after: the break-even on a 13¢ buy is 13.8 percent. On the favorite the fee moves the break-even from 88 to 88.7 percent, which turns an 88¢ contract into the equivalent of a 1.13 decimal line, about -788 in American odds. That is the number to hold against the books when they post. Re-run the arithmetic at whatever price is on the screen when you read this; the price moves and this page will not.
The Case For Van De Zandschulp, Argued Honestly
Thirteen cents may well be right. What follows is what the number would need to be wrong about, because the underdog case here is specific rather than sentimental.
It starts with the four of 17. Zverev created 17 break points against Darderi and cashed four; Darderi saw one all night and did not convert it. The man he needed 17 chances to put away had beaten him 1-6, 7-6(10), 6-0 in Rome four months earlier, per the same Sports Encounter report, so Monday was a stat and a pattern at once. A No. 1 seed who converts 24 percent of his chances is a No. 1 seed who lets sets stay close, and Van de Zandschulp has just spent a fortnight proving he wins close sets: two of the three tiebreaks against Gea, including both that decided the match, a five-setter against Bergs, and the third-set match point he saved on Monday. He won only 64 percent of the points behind his first serve on Monday, 22 points below Zverev's rate against Darderi, and still took two tiebreaks, which is the argument in one line: he does not need to hold comfortably, he needs to hold to 6-6, and a tiebreak is a much shorter bet than a match. The Alcaraz match is the callback that cuts both ways: it says he can play the best day of his life on this court against a player far better than Zverev was on Monday, and it says that day did not carry into the next round.
The other half of the argument is fatigue, and it is the reason the price is 13 and not 8. Zverev's long nights came in rounds one and two; his last two matches were straight sets, and he has the fresher legs coming out of Monday, 2 hours and 30 minutes to 5 hours and 13, even though his tournament total of 14 hours and 22 minutes is the bigger number of the two. Van de Zandschulp's five hours came on Monday, and Wednesday comes after a single day off. That is a reason for the sellers, not the buyers, and the wall at 13, 14 and 15 cents says the sellers already have it. The settlement rule leans the same way: if the Dutchman's body gives out mid-match, the contract pays Zverev.
If I had to name the one thing I would watch, it is the first set's break points. The market's 13¢ already assumes Van de Zandschulp serves well; it is priced for him to lose a good match. It is not priced for Zverev's four of 17 to become two of 17.
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What The Title Board Says About Wednesday's Winner
Kalshi's US Open men's champion board settles the rest. It, event KXATP-26USO, quotes Zverev at 27¢ bid, 28¢ ask to win the whole tournament and Van de Zandschulp at 0¢ bid, 1¢ ask. Divide each man's title price by his price to win Wednesday and you get his implied chance of winning the title given he gets through this match: Zverev's 27.5-cent midpoint over 87.5 cents is about 31 percent, and Van de Zandschulp's half-cent midpoint over 12.5 cents is about 4 percent. The board treats the survivor of this quarter very differently depending on who he is, which is the opposite of what the women's board did with Tuesday's Pegula-Navarro quarterfinal, where the same division gave both women a 16 percent conditional chance. Wednesday is worth roughly a 31 percent shot at a second major to Zverev and almost nothing to Van de Zandschulp, and the market has priced the match accordingly: the favorite's leg is the one whose title implications are being traded, and it has still drawn under 3,500 contracts.
The other Wednesday quarterfinal supplies the semifinal opponent. Khachanov is 58¢ to 59¢ to beat Blockx, the first Belgian man in a US Open quarterfinal, and the two are 2¢ to 3¢ and 1¢ to 2¢ on the title board. Alcaraz, on the other side of the draw, is 55¢ to 56¢ to win the whole thing and 78¢ to 79¢ to get past Shelton on Tuesday night. The sportsbook side of that title board is worth a look against Kalshi's: Covers' tournament odds page, updated the morning of September 7 before the round of 16 finished, had Alcaraz at a 62 percent implied chance and Zverev at 23 with the books' margin still in the numbers. Kalshi at 6 a.m. Tuesday has Alcaraz six points lower and Zverev four to five points higher. Some of that is Monday night's results, since Zverev's straight-sets win and Khachanov's five-set win over Learner Tien both arrived after Covers' pull, and some of it is the exchange being kinder to the top seed's soft half than the books were. Either way, it is the gap a reader shopping this tournament should be checking, and it is a bigger one than anything on the match market.
So the thesis holds up under its own evidence, and what would change my read is short and specific. Wednesday's order of play, due Tuesday evening, tells you whether the Dutchman gets the day session's heat after a five-hour Monday or the night's cooler air; a medical timeout in the first set, on either side, moves a 13-cent contract faster than any break point; and if the first two Zverev service games produce break chances he does not cash, the four of 17 has become a pattern the wall at 14 and 15 cents has to answer. The crowd that bought 3,800 contracts of the underdog was paying for a repeat of a Thursday in August 2024, and the quotes were pricing the Monday in September 2026 he has just played. The repeat might come. The price says it will not, and for once the price has shown its work.
As the books post and move their Zverev-Van de Zandschulp lines, the live odds screen is where to shop the moneyline across every major book against what Kalshi is showing. If pricing a single quarterfinal is not your game, OddsShopper's free expert picks cover the tournament the conventional way. For the wider market picture, the US Open men's champion board tracks the title market Zverev is 27 to 28 cents on, the US Open odds comparison across Kalshi, Polymarket and the sportsbooks maps the whole tournament, the Alexandra Eala page keeps the receipt on the last US Open match market this site priced round by round, and the daily Kalshi picks hub grades the panel's calls in public.
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These are market prices and my own reading of them, not model estimates, not predictions of fact and not financial advice. Kalshi is a CFTC-regulated event-contract exchange (18+; availability varies by state). Prices quoted are the snapshot named above and will have moved by the time you read this.
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