Kalshi's market on Wednesday's US Open men's singles quarterfinal between Karen Khachanov and Alexander Blockx quotes Khachanov at 58¢ bid, 59¢ ask, and Blockx at 41¢ bid, 42¢ ask, as of September 8, 2026, at 6:02 a.m. ET. Read as probabilities, the 30-year-old Russian, ranked No. 50 and unseeded, is a 58 to 59 percent favorite over the 21-year-old Belgian who is seeded 28th and who told reporters after Monday's win that he had been "really close to retiring" with a rib injury. That last clause is the whole market. Of Wednesday's two quarterfinals, the other one has Alexander Zverev at 87¢ to 88¢ against Botic van de Zandschulp, so this is the match the market cannot call, and the reason has less to do with tennis than with a rib nobody outside Blockx's camp can see.
The price did not start here. It opened Monday night at 80¢ into an empty book, got sold down to 54¢ inside an hour, and found 55 to 57 by 11 p.m. ET. The net of every cent since has been bought: the crowd took more than 16,000 contracts of Khachanov in eight hours, and the price moved two cents. Where the buying stops is written on the order book in a number I will get to, and it says Wednesday's least-confident quarterfinal is a lot more settled than 58 to 42 sounds.
The Quick Answer
Khachanov is the favorite at 58¢ to 59¢ on Kalshi and Blockx the underdog at 41¢ to 42¢ for Wednesday, September 9; the order of play had not been posted when this went up. My read is that the gap is an injury premium. Blockx said Monday night he was close to retiring with a rib injury, the overnight crowd bought Khachanov on that sentence, and the price still only moved two cents from its 11 p.m. level, because a 74,688-contract wall is sitting on the offer at 59¢. How the price got there, what a Blockx retirement would do to a 42-cent contract, and what the title board says about whoever wins are all below.
How Khachanov And Blockx Got To Wednesday
Start with the one fact the two men share, because they have never played each other on tour. Blockx won the 2023 Australian Open boys' title, and the player he beat in that final was Learner Tien. On Monday night Khachanov needed five sets, three hours and 50 minutes and 323 points to get past the same Tien, 7-5, 4-6, 6-7(6), 6-1, 6-4, from two sets to one down. It is a transitive read across three and a half years and a junior draw, which is to say it is barely a read at all, but it is the only line between them, and it is part of why a 28 seed with a rib is not priced like an accident.
Khachanov's side of the bridge is the pedigree. The ATP Tour's own recap has him summing up Monday as "one extra ball coming back, one extra ball." It is his seventh major quarterfinal, his first since Wimbledon 2025 and his deepest run in New York since the 2022 semifinal, and his second round was the bigger scalp: he put out No. 3 seed Felix Auger-Aliassime 6-7, 6-3, 6-2, 6-2 on Thursday, the upset that emptied the top of this quarter of the draw. He is ranked No. 50 and unseeded.
Blockx's side is the rib, and two of the numbers in it argue against each other; the market has picked one. He beat No. 24 seed Francisco Cerundolo 6-3, 4-6, 7-5, 7-5 on Monday in three hours and 15 minutes, saved 14 of the 17 break points he faced, including a 0-40 hole at 5-5 in the third set, and hit 36 winners, and by the ATP Tour's own match report he was hurting from the second game on. "I was just holding on to be honest," he said afterward. "Even though I won that first set 6-3, it could have been the other way round." A doctor gave him medication during the match, "the doctor gave me some magical medication and that kept me going," and the quotes that moved the market came in the AFP write-up: "I was really close to retiring, to be honest," and "if I would have lost the third set, I think the chances were really high of me retiring." He added the line a trader hears loudest: "I had medication. So if you feel that much pain while having a lot of medication, that's not a good sign." The 14 of 17 is the case for the 42¢ contract; that sentence is the case against it, and 41 to 42 is where the market weighed them.
The win made him the first Belgian man to reach a US Open quarterfinal, a claim the ATP and AFP both make, and the youngest Belgian man in a major quarterfinal in the Open era; only three Belgian men had reached the last eight at any Slam before him, per the ATP. He started 2026 outside the top 100 and had to qualify for the Australian Open. He came into New York ranked No. 34, and his path here ran through No. 5 seed Flavio Cobolli in the third round before Cerundolo. Both men are on the same short turnaround, and until the tournament posts Wednesday's order of play the recovery clock is unknown to everyone.
What Kalshi's Price Says, And How It Got There
Kalshi lists the match as a pair of yes-or-no contracts, one per player, under event KXATPMATCH-26SEP09KHABLO; each pays $1 if its man wins. Here is where the four men's quarterfinals stood at the same 6:02 a.m. ET snapshot, Tuesday's two matches included because they show what a confident quarterfinal price looks like next to this one.
| Quarterfinal | Day | Kalshi price (bid / ask) |
|---|---|---|
| Carlos Alcaraz Vs Ben Shelton | Tuesday | Alcaraz 78¢ / 79¢; Shelton 21¢ / 22¢ |
| Frances Tiafoe Vs Alex Michelsen | Tuesday | Tiafoe 57¢ / 58¢; Michelsen 42¢ / 43¢ |
| Alexander Zverev Vs Botic Van De Zandschulp | Wednesday | Zverev 87¢ / 88¢; Van de Zandschulp 12¢ / 13¢ |
| Karen Khachanov Vs Alexander Blockx | Wednesday | Khachanov 58¢ / 59¢; Blockx 41¢ / 42¢ |
Tuesday's two prices are the September 8, 6:02 a.m. ET snapshot and will have resolved by the time Wednesday's matches start; they are here for the comparison, not the trade.
The row worth reading is the second one. Tiafoe against Michelsen is a cent closer to even than this match, so Khachanov-Blockx is not quite the closest price of the four; it is one of only two quarterfinals the market treats as competitive, and by Wednesday the Tiafoe match will have been decided. Both spreads are one cent wide, which on Kalshi means buying both sides at the ask costs $1.01 for a contract pair that pays exactly $1. The market's take on the two matches is the same: someone is a modest favorite, and the sellers on each side are close enough together that nobody is guessing.
It did not start that way. The Khachanov contract listed at 9:50 p.m. ET on Monday night, and the first prints were an empty-book mess: a handful of lots at 80¢ in the first ten minutes, a 50¢ trade at 10:21 p.m., and a 54¢ fill by 10:43. Blockx's first real trade was 209 contracts at 46¢ at 10:24 p.m. By 11 p.m. the book had found 55 to 57 on Khachanov and 43 to 46 on Blockx. The 58¢ level was first bought in size just after midnight, a 1,507-contract lot at 12:25 a.m. among roughly 2,300 contracts that printed, meaning traded, at 58¢ before 1 a.m., and it did not hold; the price sagged back to 57¢ and sat there for four hours. The morning block did hold: between 5:18 and 5:49 a.m. another 2,350 contracts went through at 58¢, a 1,667-lot at 5:23 a.m. the biggest of them, and the first 59¢ prints of the market's life came at 5:40 a.m. The last fill before the snapshot was 59¢.
The direction of the trading is not subtle. Of the 16,446 Khachanov contracts that traded, 16,090 were bought by someone lifting the offer, paying whatever a seller was asking, and 356 were sold into a bid. On the Blockx contract, 6,454 traded, and the takers sold him more often than they bought him: 3,834 contracts sold against 2,620 bought. Add the two legs and roughly 19,900 contracts of aggressive money went Khachanov's way overnight against about 3,000 that went Blockx's. Picture a crowd reading the same medication quotes I read, and buying. That took the price from its 11 p.m. level of 55 to 57 up to 58 to 59. Which raises the question the rest of this page is about: why only two cents?
The Order Book: Where The Khachanov Buying Stops
Kalshi's order book, the list of resting orders waiting to be filled, answers it. On the Khachanov contract, the best bid at 58¢ has 3,808 contracts behind it. The best offer at 59¢ has 74,688. That is the wall, the single most lopsided number on this market. Every one of those 74,688 contracts is someone willing to sell Khachanov at 59¢, which is the same thing as someone willing to back Blockx at 41¢. Add the 6,020 contracts bid for Blockx directly at 41¢ on his own leg and there are more than 80,000 contracts of patient money waiting to take the Belgian at 41 cents, against about 10,000 waiting to take the Russian at 58.
Whoever is behind the wall, and market makers quote in this kind of size as a matter of course, the effect is the same: Khachanov does not print 60¢ until 74,688 contracts change hands at 59, for as long as the order stays there; a resting offer is a quote, not a promise, and it can be pulled the moment the order of play or a practice report changes the rib story. The overnight crowd bought 16,000 in eight hours. The crowd chased the favorite all night and ran into a seller that did not blink. Behind the wall it stays thick: 5,266 contracts offered at 60¢, then 39,929 at 61¢ and 49,152 at 62¢. Compare the Blockx side, where the front of the book is thin, 6,328 at 42¢ before 23,955 at 43¢, and the shape of the market is clear. Buying Blockx a cent or two higher is easy. Buying Khachanov a cent higher is very hard. The book is boxed on the other side too: about 76,000 contracts are bid for Khachanov between 55¢ and 57¢, so the same market that will not let him print 60 will not let him sag to 54 either. That is a market that has decided the range and is arguing over two cents inside it, and the bigger pile of resting money sits on the Belgian's side of the ledger, whatever the takers did overnight.
Worked Example: 100 Contracts At 42¢
For a reader thinking about what 42¢ buys, the fee matters at this price more than anywhere on the board, because Kalshi's fee is largest on coin-flip contracts. One hundred contracts of Blockx at 42¢ cost $42 plus a $1.71 fee under Kalshi's 7 percent formula, so the trade breaks even if he wins about 43.7 percent of the time, not 42. Khachanov at 59¢ carries a $1.70 fee on 100 contracts and breaks even at roughly 60.7 percent. Our fee-schedule page walks the arithmetic; the short version is that the one-cent spread is not the only cent between you and fair value here, and on a match this close a cent and a half is a large share of the argument. Tennis.com's match page shows the same 58-42 split, though projections like that usually take their cue from the same market, so treat it as an echo rather than a second opinion. Neither number prices the rib on its own.
What The 42 Cents Is Really Paying For
Here is what the market is actually pricing, in the order I weight it. First, the rib. Blockx said he was close to retiring, said the medication was not masking the pain, and then had a night's sleep and a day off before a Wednesday match against a man who is 6-foot-6 and hits through the court. Nobody who bought Khachanov at 57¢ in the middle of the night knows how that rib feels on Wednesday morning. They are pricing a possibility, and 41 to 42 cents on a 28 seed who has just beaten a No. 5 seed and a No. 24 seed back to back is what the possibility costs. The contract's own fine print sharpens the point: Kalshi's rules say each market settles on the winner "after a ball has been played," and a withdrawal before the first ball is served resolves at a fair price instead, so the 42¢ is not a bet that Blockx shows up. It is a bet that he starts and finishes, because a retirement in the second set pays Khachanov's side the full dollar. Strip the injury out and the seed, the age, the ranking gap in Blockx's favor, and the form against Cobolli and Cerundolo would put him closer to even. The two-cent overnight move and the eight-and-a-half-point gap from even are the injury premium, and it is not hard to see why the market charges it.
Second, the mileage. Khachanov played 323 points and nearly four hours on Monday; Blockx played three and a quarter hours through the pain. A 30-year-old coming off a five-setter and a 21-year-old coming off a four-setter with a rib is a wash on paper, and the market treats it as one, but it is the reason both prices sit where they do rather than farther apart. Khachanov has done this before, a 2022 semifinal here and six previous major quarterfinals; the pedigree is what the 58 buys. Blockx saved 14 of 17 break points on Monday and dug out of 0-40 at 5-5 in the third with a bad rib. That is what the 42 buys. Neither man has a set of evidence against the other, because they have never played.
The counter to the market's read is the one I keep coming back to: Blockx's own numbers say the rib did not stop him from doing the hard things. Fourteen of 17 break points saved is not a stat line from a player who was holding on; it is one from a player who served his way out of trouble for three hours. If the treatment works and the pain is manageable, the 41¢ side is paying an injury premium for an injury that did not show up on the scoreboard. The counter to that counter is his own sentence about the medication, and for now the market believes him. What I would watch is the Wednesday order of play and the first two service games: a rib shows up on the serve before it shows up anywhere else, and the market that took eight hours to buy two cents will move faster than any of us can type if it does.
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What The Title Board Says About Wednesday's Winner
Kalshi's US Open men's champion board, event KXATP-26USO, puts the winner of this match in context. Khachanov is quoted at 2¢ bid, 3¢ ask to win the tournament; Blockx is 1¢ bid, 2¢ ask, level with Alex Michelsen and a cent above Van de Zandschulp's 0¢ to 1¢. Divide each man's title price by his price to win Wednesday and you get his implied chance of lifting the trophy given he gets through: Khachanov's 2.5-cent midpoint over 58.5 is about 4 percent, and Blockx's 1.5 over 41.5 is about 3.6 percent. Whoever wins on Wednesday, the board says he is somewhere between a 23-to-1 and a 28-to-1 shot from there, and the reason is one row up on the same board. Alexander Zverev is 27¢ to 28¢ to win the title and 87¢ to 88¢ to beat Van de Zandschulp, which makes him the likely semifinal opponent for the winner of this match. In a four-quarterfinal draw that leaves Tuesday's two winners for the other semifinal, and Outlook India's quarterfinal report confirms the Alcaraz-Shelton winner meets Tiafoe or Michelsen there; Carlos Alcaraz is 55¢ to 56¢ to win it all from that half. The market is pricing this quarterfinal as the match that decides who gets to lose to Zverev, and it is pricing that outcome the same for both men.
That is the frame that makes the 58-to-42 split easier to read. The market does not believe Wednesday's winner is going far. It is arguing about a single match between two men who have never played, one of whom may or may not be whole, and a single match with a hurt player in it is the hardest thing on the board to price. The crowd took one side of that argument overnight in size. A wall of resting money took the other and has not moved. An 80-cent opening print into an empty book, a sell-off to 54, two cents of buying since 11 p.m., and 74,688 contracts saying not a penny more: that is what a market looks like when it knows exactly how much it does not know.
As the books post their Khachanov-Blockx lines, the live odds screen is where to shop the moneyline across every major book against what Kalshi is showing. If pricing one quarterfinal is not your game, OddsShopper's free expert picks cover the tournament the conventional way. For the wider picture, the US Open odds comparison across Kalshi, Polymarket and the sportsbooks maps the whole board, the men's champion board page prices the whole bracket, the Cincinnati final page keeps the receipt on the last Grand Slam-level match we priced this way, our Kalshi sports guide covers how the match contracts settle, 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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