The Quick Answer
Ben Shelton beat Frances Tiafoe 4-6, 6-3, 6-3, 7-5 in Friday's all-American US Open men's semifinal, in 3 hours and 17 minutes at Arthur Ashe Stadium, and Kalshi settled his contract at $1.00 and Tiafoe's at zero at 11:06 p.m. ET on September 11. The Tiafoe contract that held 28¢, give or take a cent, from Wednesday breakfast to Friday's first ball printed 51¢ at 8:28 p.m., with Tiafoe a set up, and 1¢ at 10:59 p.m. The 33,333 contracts one fill took at 28¢ on Wednesday were worth $7,000 more than they cost at the best bid the log shows, 49¢ at 8:29 p.m., and anyone still holding them at 11:06 collected nothing. How every side contract graded, and what the title board did to Shelton two days later, is below.
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The Match: A Set Down, Then 20 Aces
On Wednesday this page said the one thing to watch was the first set, because the only match Tiafoe had ever taken from Shelton in New York was a five-setter that began with Shelton a set up and ended with him out of legs. Friday inverted it. Tiafoe took the first set and Shelton took the next three, and the reason is in the serving numbers, so the tennis comes first.
ESPN's match report has the first set as the one Tiafoe played cleanly, three unforced errors to Shelton's 14, and the break coming on a Shelton double fault at 4-4. From there, per ESPN, Shelton's serve took over: 144 and 140 mph deliveries with the new balls at 3-all in the second set, 20 aces for the match, and a Tiafoe second serve that won 69 percent of its points in the first set and 28 percent of them after it, 11 of 39. The third set ended on a 15-minute, 20-point game that Tiafoe finished with a forehand into the net. NBC Sports has Tiafoe with three aces to Shelton's 20 and the fourth set decided from 5-5; Yahoo's live blog has Shelton serving first in that set and saving three break points in the opening game, holding every service game after it, and the match ending on a Tiafoe double fault with Tiafoe serving at 5-6.
"Ben played well tonight. Served really well tonight, which made it really tough on me," Tiafoe told ESPN. Shelton, to the crowd: "I'm going for it here, and I'm going to leave it all on the court. I hope you guys come and back me. Let's do it for the USA."
Forty games, 23 of them Shelton's, and a four-set match. Hold on to both numbers; between them they graded every side contract on the match. The head-to-head is now 4-1 Shelton, and the New York series 2-1. Tiafoe, per ESPN, is 0-3 in US Open semifinals. Shelton, per ESPN, became the first Black American man in a US Open final since Arthur Ashe in 1972 and the first in any major final since MaliVai Washington at Wimbledon in 1996, and drew the man Wednesday's board had been worried about all along: Alexander Zverev, who beat Karen Khachanov 6-3, 7-6(7), 7-6(6) in the afternoon semifinal and led Shelton 5-0.
How The Match Contract Settled
Kalshi lists each man as his own yes-or-no contract under the event ticker KXATPMATCH-26SEP11TIASHE, and the Shelton contract's primary rule reads, in full: "If Ben Shelton wins the Tiafoe vs Shelton professional tennis match in the 2026 US Open Men Singles Semifinal after a ball has been played, then the market resolves to Yes." A ball was played, Shelton won, and per Kalshi's public market data the exchange closed both contracts at 11:03:27 p.m. ET and finalized them at 11:06:28 p.m., three minutes later. The withdrawal and postponement clauses Wednesday's edition walked through, after two quarterfinal marathons, never came into it. The final print:
| Contract (KXATPMATCH-26SEP11TIASHE) | Final price | Settled | Contracts traded, lifetime | Open interest at close |
|---|---|---|---|---|
| Ben Shelton Wins | 99¢ | $1.00 | 8,110,785 | 4,818,397 |
| Frances Tiafoe Wins | 1¢ | $0.00 | 11,214,953 | 5,558,947 |
Final price is the last trade on each leg before the close at 11:03:27 p.m. ET on September 11, 2026; settlement, lifetime volume and open interest are from Kalshi's public market data after finalization. The Tiafoe leg had traded 68,113 contracts when this page was first written on Wednesday afternoon.
The row to sit with is the volume. Wednesday's page called 68,113 Tiafoe contracts a lot, because 33,333 of them had arrived in one print. By the close the Tiafoe leg had traded 11.2 million and the Shelton leg 8.1 million, and 10.2 million of Tiafoe's went through from 6:30 p.m. Friday onward. The whole pre-match market on the underdog, all of Wednesday, Thursday and Friday afternoon, was 1,001,089 contracts, about nine percent of what the contract did in its life. The wall this page described on Wednesday, 129,266 contracts offered within two cents of the ask, was a footnote by the second set.
The Price History: 51¢ At 8:28 P.m., 1¢ By 10:59
The price history does not carry the score, only its shape. The times below are when money moved on Kalshi's public trade log, and the right-hand column maps them to the match reports; the set times are the price history's, not the umpire's.
| Time (ET, Sept. 11) | Shelton | Tiafoe | What the price was reacting to |
|---|---|---|---|
| 7:43 P.m. | 73¢ | 29¢ | Last prints before the first ball |
| 8:24 P.m. | 67¢ | 34¢ | The break at 4-4 in the first set, on a Shelton double fault |
| 8:28 P.m. | 50¢ | 50¢ | First set to Tiafoe, 6-4; Tiafoe's high print, 51¢ |
| 8:36 P.m. | 65¢ | 35¢ | Buyers back on Shelton inside eight minutes |
| 9:00 P.m. | 73¢ | 27¢ | Back to Wednesday's price, in the second set |
| 9:29 P.m. | 84¢ | 17¢ | Second set to Shelton, 6-3 |
| 9:59 P.m. | 89¢ | 11¢ | Third set to Shelton, 6-3, after the 20-point game |
| 10:10 P.m. | 86¢ | 15¢ | Shelton saving three break points in the opening game of the fourth |
| 10:50 P.m. | 85¢ to 88¢ | 12¢ to 15¢ | Fourth set on serve |
| 10:57 P.m. | 94¢ | 7¢ | Shelton holds for 6-5 |
| 10:59 P.m. | 99¢ | 1¢ | Match point: Tiafoe broken at 5-6 on a double fault |
| 11:03:27 P.m. | closed, paid $1 | closed, paid $0 | Contract closed; finalized 11:06:28 p.m. |
Prices are the last trade at or before each clock time on each leg, from Kalshi's public trade log. The Shelton leg printed 123,965 contracts at 99¢ from 10:58:42 p.m. on; the Tiafoe leg printed 53,655 at 1¢ from 10:58:38 p.m.
The row that decides this page is 8:28 p.m., because it is the only minute in the life of the market when the two contracts were the same price. Tiafoe had served out the first set, and for one print Kalshi had the semifinal as a coin flip: Shelton 50¢, Tiafoe 50¢, with the Tiafoe leg touching 51¢ and the Shelton leg 49¢ inside that minute. That is a 17-cent move on the underdog in four minutes, and a 23-cent move off the price the contract had held for two and a half days. The Tiafoe contract traded 155,455 contracts in the 8:28 minute alone, more than twice what it had traded in its entire life when Wednesday's page went up.
Then the buyers came back for the favorite. Eight minutes later Shelton was 65¢. At 9:00 p.m. he was 73¢, which is where Wednesday, Thursday and Friday afternoon had priced him, and the second set had not yet ended. From there the price history is a staircase: 84¢ when the set did end, 89¢ after the third, one honest dip to 78¢ in the 10:10 minute when Shelton faced three break points in the opening game of the fourth set, and the climb from 94¢ to 99¢ across the two and a half minutes from 10:57 p.m. to 10:59 p.m. that covered Shelton holding for 6-5 and Tiafoe's double fault. The biggest Shelton fill once the match was on was a buy, 47,500 contracts at 73¢ at 9:05:51 p.m., five minutes after the price got back to where it started. The biggest Shelton sell was 40,444 contracts at 60¢ at 8:38:37 p.m., ten minutes after the first set, and whoever sold those saw the contract pay $1.00 two and a half hours later.
What Happened To The 33,333 Contracts
The open question on Wednesday was this: whether the fill of 33,333 Tiafoe contracts at 28¢ at 10:18:26 a.m., a $9,333 position in one print, was the same account that took about 33,000 Michelsen contracts at 3 a.m. on Monday, and whether it knew something. Kalshi's public trade log still does not say who it was, and I will not guess. What the log does say is what the position was worth, minute by minute, and how much company it had.
It had a great deal of company. From the moment that fill went through until 6:30 p.m. Friday, 896,363 more Tiafoe contracts were bought by takers at the ask, against 59,959 sold. The 33,333 was not the biggest print on the leg for long: at 12:25:14 p.m. on Friday a single fill took 87,750 Tiafoe contracts at 28¢, $24,570 in one print, and three more fills of 13,793, 13,793 and 14,286 contracts went through at 28¢ within three seconds of each other at 4:34 p.m. Across the whole pre-match market, 94 percent of the Tiafoe leg's 1,001,089 contracts were buyer-initiated, at a volume-weighted average of 28.02¢. The Shelton leg was the mirror: 94 percent of its 509,321 pre-match contracts were buys too, the largest of them 49,076 contracts at 73¢ at 6:17:47 p.m. Friday, an hour and a half before the first ball. Both crowds were buying from makers, and the makers' price never moved: 26¢ to 29¢ on Tiafoe from Wednesday breakfast to Friday's first ball, and 28¢ on nearly every print.
Then Friday night, and the two endings the log allows. On paper, at the 8:28 p.m. print, 33,333 contracts bought at 28¢ were worth about $16,700 at 50¢ and $17,000 at 51¢, against $9,333 paid. In practice, the bid side is what a seller gets, and the log shows what it held: between 8:24 and 8:36 p.m., takers sold 360,727 Tiafoe contracts into the bids, 298,859 of them at 45¢ or better and 19,921 at 50¢ or better. The largest single sell in that window was 17,000 contracts at 49¢ at 8:29:01 p.m. A holder of the 33,333 who sold there, at 49¢, cleared about $7,000 before fees and about $5,950 after paying Kalshi's taker fee on both sides. A holder who did not sell was $9,333 down, plus the $470 fee on the way in, at 11:06 p.m. The log cannot say which ending the 33,333 got. It can say that the window to take the first was about 12 minutes wide, that some 300,000 contracts of Tiafoe went out through it at 45¢ or better, and that seven and a half million Tiafoe contracts were bought by takers over the whole night, most of them after it closed.
That last number is the one that changes what Wednesday's page thought it was looking at: in dollars, the in-play Tiafoe buying was nearly seven times the entire pre-match market on him, which came to about $280,000. A 33,333-contract print at 10:18 on a Wednesday morning is the loudest thing on the log for two days and a rounding error by 9 p.m. Friday, and the Michelsen page's 3 a.m. buyer was the same story a round earlier.
The Side Contracts, Graded
The pre-match edition quoted no side markets, so this is a straight grade from Kalshi's public data, by ticker, against 40 games, 23 to 17, four sets.
| Contract | Rule | Result | Contracts traded, lifetime |
|---|---|---|---|
| KXATPSSPREAD-26SEP11TIASHE-SHE2 | Shelton wins by over 1.5 sets | Yes | 198,965 |
| KXATPSSPREAD-26SEP11TIASHE-TIA2 | Tiafoe wins by over 1.5 sets | No | 14,960 |
| KXATPEXACTMATCH-26SEP11TIASHE-SHE31 | Shelton wins 3-1 | Yes | 349,814 |
| KXATPEXACTMATCH-26SEP11TIASHE-SHE30 | Shelton wins 3-0 | No | 229,771 |
| KXATPEXACTMATCH-26SEP11TIASHE-SHE32 | Shelton wins 3-2 | No | 176,970 |
| KXATPEXACTMATCH-26SEP11TIASHE-TIA32 | Tiafoe wins 3-2 | No | 116,775 |
| KXATPEXACTMATCH-26SEP11TIASHE-TIA31 | Tiafoe wins 3-1 | No | 50,930 |
| KXATPEXACTMATCH-26SEP11TIASHE-TIA30 | Tiafoe wins 3-0 | No | 114,697 |
| KXATPGTOTAL-26SEP11TIASHE-35 | Over 34.5 games | Yes | 143,897 |
| KXATPGTOTAL-26SEP11TIASHE-40 | Over 39.5 games | Yes | 450,445 |
| KXATPGTOTAL-26SEP11TIASHE-45 | Over 44.5 games | No | 114,212 |
| KXATPGSPREAD-26SEP11TIASHE-SHE2 | Shelton -1.5 games | Yes | 49,653 |
| KXATPGSPREAD-26SEP11TIASHE-SHE5 | Shelton -4.5 games | Yes | 353,560 |
| KXATPGSPREAD-26SEP11TIASHE-SHE8 | Shelton -7.5 games | No | 29,826 |
| KXATPTOTALSETS-26SEP11TIASHE-4 | Over 3.5 sets | Yes | 331,462 |
| KXATPTOTALSETS-26SEP11TIASHE-5 | Over 4.5 sets | No | 86,954 |
Results and lifetime volumes from Kalshi's public market data after finalization; every contract in the five side series closed between 11:05:53 and 11:05:56 p.m. ET. Shelton wins 3-1 was the busiest exact-score contract and the one that paid; over 39.5 games was the busiest contract of the 16.
The row worth a sentence is the games total, because it was decided by one hold. Twenty-eight games through three sets plus a 7-5 fourth is 40, exactly what over 39.5 needed. The contract was decided a few minutes before the match was: once Tiafoe held from 4-5 down for 5-5, the set could not end in fewer than 12 games, and 28 plus 12 is 40. Had Shelton broken in that game instead of two games later, the match ends 6-4 at 38 games, and the busiest side contract on the board pays the other way. The exact-score 3-1 contract, 349,814 contracts, paid on the one scoreline that let Tiafoe have his set and nothing else.
The Title Board: 37¢ On Wednesday, 44¢ On Friday Night, 1¢ On Sunday
Here is the callback this page owes, because the argument Wednesday's edition made was not about Friday at all. It said the semifinal was priced within a fifth of a cent of the sportsbooks and nothing on the log argued with it; the stretch was one match further on, where Kalshi's title board, 37¢ to 38¢ on Shelton, divided by the 72¢ to 73¢ match price, made him a coin flip in a final against a man who was 5-0 against him. Dividing one price by another is arithmetic, not a forecast, and Friday and Sunday delivered the numbers to check it against.
Friday night, Kalshi's Shelton title contract went from 37¢ in the afternoon to 31¢ around the first ball and 44¢ by 11 p.m., with 160,261 contracts changing hands in the hour after the match and the price holding 42¢ to 44¢ through Saturday. Zverev's, 43¢ bid and 44¢ ask when Wednesday's page went up, was 58¢ by the same hour, after his straight-sets win over Khachanov in the afternoon. With two men left, the title contract and the final's match contract are the same bet, priced on the same afternoon, so the board's conditional coin flip, 52 percent for Shelton if he got there, became 44¢ against 58¢ the moment he did. The market moved toward the head-to-head record, not away from it, as soon as the semifinal stopped being a variable. Tiafoe's title contract, 10¢ to 11¢ on Wednesday, settled at zero at 11:25 p.m. Friday.
Then Sunday. Zverev beat Shelton 6-3, 7-6(2), 5-7, 6-2 for the title, and that page has the full trade log of the final; the short version for this one is that Shelton's title contract was 43¢ at 2 p.m., 25¢ by 3 p.m., 14¢ by 5 p.m. and 1¢ at 6 p.m., and paid nothing. The record was 6-0 by dinner. The reader Wednesday's page described, who believed Shelton beat Tiafoe and would be an underdog to Zverev, and who therefore wanted the match contract rather than the title contract, was paid exactly as described, and the arithmetic is in the worked example below.
A Worked Example: What 73¢ And 38¢ Paid
On 100 contracts, the arithmetic reads like this. Shelton's match contract at the 73¢ ask cost $73, carried a $1.38 taker fee under Kalshi's published fee schedule, and returned $100 at 11:06 p.m. Friday: $25.62 clear. His title contract at the 38¢ ask cost $38, carried a $1.65 fee, and returned nothing on Sunday: $39.65 gone. Tiafoe's match contract at 28¢ cost $28, carried a $1.42 fee, was worth $50 for one print at 8:28 p.m., and returned nothing. As of September 13, 2026, at 11 p.m. ET, every one of those contracts is finalized and none of them can be traded; the numbers are history, not a quote.
The stretch was where the page said it was. What the page did not know, and said it did not know, was whether the stretch would close in Shelton's favor or against him; it closed against him in four sets.
What Wednesday's Read Got Right, And What It Missed
Wednesday's page did not call the match, and it should be graded on what it did say. The first claim was that the price was right, and it was: a 72¢ to 73¢ favorite won, in four sets, and the sportsbook moneyline of -300 and +240 it quoted implied the same 72 and 28 once the margin came out. The second was that the stretch sat in the final, not the semifinal, and Sunday closed that stretch the way the head-to-head said it would. The third was that the first set was the thing to watch, and the first set went to Tiafoe, the contract went to 51¢, and it did not matter, because the 2024 loss the page kept coming back to was a 21-year-old running out of legs in a fifth set, and Friday's match ended in the fourth with Shelton's serve still the thing Tiafoe could not touch.
What the page missed was scale. Wednesday's edition treated a 33,333-contract fill as the event of the market and a 129,266-contract wall as the thing that would decide the price, and on Wednesday, with 68,113 contracts traded, both were true. By Friday night neither was. Ten million Tiafoe contracts traded in play, the price moved 17 cents in four minutes on a single set, and the wall that had held 28¢ through 33,333 contracts held nothing at all once the set was over. The lesson, carried to the Michelsen page a round earlier and here again, is that a pre-match tennis market on Kalshi is a small, patient thing, and the in-play market is a different animal that eats it. The pre-match print tells you who was buying while the crowd slept. It does not tell you what the crowd will do when it wakes up.
Where This Leaves The Two Americans
Shelton's semifinal contract paid and his final contract did not. He beat the defending champion, then a man in his third US Open semifinal, then lost his sixth straight to Zverev, the No. 1 seed. The drought that began when Andy Roddick won here in 2003 is intact, and Shelton is 23. Tiafoe's price told its own story: 28¢ for two and a half days, 51¢ for a minute, 1¢ by 10:59 p.m., and a third US Open semifinal that ended with a double fault rather than a fifth set. The next time these two draw each other, the head-to-head will read 4-1 and the New York series 2-1, and the price history of this one will read the way it should: the favorite lost the first set, the market priced a coin flip for one minute, and the serve decided the rest.
Kalshi's settlement rules and review window explain why the contracts closed at 11:03 and paid at 11:06. As the books post next week's ATP lines, the live odds screen is where to shop a tennis moneyline across every major book against what Kalshi is showing. If pricing a single match is not your game, OddsShopper's free expert picks cover the sport the conventional way. For the wider board, the US Open odds comparison across Kalshi, Polymarket and the sportsbooks maps the whole tournament, and the daily Kalshi picks hub grades the panel's calls in public.
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Prices quoted are the settled prints named above; the market is closed and will not move.
