The Quick Answer
Rain stopped Kimberly Birrell vs Petra Marcinko at the US Open on Sunday night with the second-set tiebreak frozen at 3-3. Kalshi's Set 2 Winner market froze with it, and by Monday morning the book had both women at a coin flip, a few cents either side of 50. That was the honest price: the set was as few as four points from over, and nothing in the first set or the rankings moves a four-point coin flip. The board below is the overnight snapshot, priced before play resumed.
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What The Rain Froze
Sunday night's storm at Flushing Meadows suspended first-round matches on the roofless outer courts. One of them was this women's singles first-round match between Australia's Kimberly Birrell and Croatia's Petra Marcinko, and it stopped in the one spot a set market can least tolerate: mid-tiebreak. Australia's ABC reported the freeze precisely: Marcinko took the first set, the second reached 6-6, and "the tiebreaker was locked at 3-3" when the players walked off around 8 p.m.
A tiebreak is first to seven, win by two. From 3-3 each woman needed four points before the other did, and that was the entire remaining question. Each name is its own yes/no contract under the event ticker KXWTASETWINNER-26AUG30BIRMAR-2, paying out in full to whoever wins the set, whatever happens to the match afterward, and settling when the set does.
The Board
As of 9:15 a.m. ET on Monday, Aug. 31, 2026:
| Contract | Bid | Ask | Last trade | Contracts (24h) | Open interest |
|---|---|---|---|---|---|
| Birrell Wins Set 2 | 44¢ | 55¢ | 36¢ | 110,102 | 44,424 |
| Marcinko Wins Set 2 | 43¢ | 57¢ | 56¢ | 98,465 | 56,510 |
Both last trades printed away from 50, but the resting book Monday morning bracketed each name around a coin flip with a wide spread on either side, because nobody quotes a sleeping tiebreak tightly. More than 208,000 contracts changed hands in 24 hours on a market that could have as few as four points of tennis left in it. Buying either name at the ask meant paying above a true coin flip for the right to trade a frozen market, which is why patient traders quote a book like this rather than cross it.
Why The First Set Didn't Move The Price
Marcinko, a former junior world No. 1, had been the form player: her first WTA title came in Rabat this May, and she took the first set 6-3. Birrell, who beat then-fifth-seed Jessica Pegula at this year's French Open, dragged the second set to 6-6.
None of that survives a tiebreak at 3-3. A set lead matters enormously for the match and not at all for this contract, which pays whoever takes the set even if she loses the match afterward. The rankings gap, Marcinko at No. 53 in early August against Birrell's No. 74 in June, is worth a few cents across a full set; across four points it is nearly invisible. That is why the market showed no favorite, and it is the lesson every short-fuse Kalshi market teaches: the contract pays the literal question and nothing else.
Bottom Line
The overnight book settled on the only honest read of a frozen tiebreak: a coin flip with a wide spread attached, so anyone who wanted to disagree paid for the privilege. Play was scheduled to resume Monday, and the contract settled with the set. Kalshi listed markets across this US Open, and our comparison of US Open odds across Kalshi, Polymarket, and the sportsbooks maps that wider board.
New York's attorney general sued Kalshi on July 31 alleging it operates as an unlicensed gambling platform, and that fight is pending. We track where prediction markets stand legally; check your state before you trade.
If pricing four points of somebody else's tiebreak isn't your edge, OddsShopper's free expert picks work full matches with real research behind them, and our experts' US Open betting picks cover this tournament the conventional way.
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