The Quick Answer
Rain stopped Kimberly Birrell vs Petra Marcinko at the US Open on Sunday night with the second set locked at 6-6 and the tiebreak frozen at 3-3, so Kalshi's Set 2 Winner market spent the night as few as four points from resolution in either direction. The market's two contracts have traded a combined 208,566 contracts in 24 hours, and as of 9:15 a.m. ET Monday both names are quoted as a coin flip: Birrell 44¢ bid / 55¢ ask, Marcinko 43¢ / 57¢. How the set got here, what those wide quotes actually offer you, and what happens to the contract when play resumes Monday are all below.
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The Purest Price On The Board
Most prediction markets ask you to weigh months of evidence. This one asks you to price four points of tennis, and that is the thesis of this page: rain accidentally manufactured the purest market object Kalshi has listed all week. Sunday night's storm at Flushing Meadows suspended seven first-round matches on the roofless outer courts, and one of them, a US Open women's singles Round of 128 match between Australia's Kimberly Birrell and Croatia's Petra Marcinko, stopped in the one spot a set market can least tolerate: mid-tiebreak. Kalshi has listed markets across this US Open, and our comparison of US Open odds across Kalshi, Polymarket, and the sportsbooks maps that wider board; this page is about the strangest single contract on it. Australia's ABC reported the freeze precisely: Marcinko took the first set, the second set 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 points, win by two. At 3-3, each woman needs four points before the other gets four. That is the entire remaining question, and the market's overnight prices say exactly that and nothing more. I'll show you further down why the first set, the rankings, and everything else you might research are almost beside the point for this contract; first, the mechanics, because they decide what you're actually holding.
How A Kalshi Set Winner Market Settles
Kalshi lists each name as its own yes/no contract under the event ticker KXWTASETWINNER-26AUG30BIRMAR-2. The Birrell contract's rule is plain: if Kimberly Birrell wins set 2 of this match in the 2026 US Open Women's Singles Round of 128, it resolves to Yes at $1.00; otherwise it goes to zero. The Marcinko contract mirrors it. A price in cents is the crowd's probability, so a 50¢ contract is a stated coin flip. One wrinkle worth knowing: the exchange originally expected this market to expire Sunday afternoon, before rain rewrote the schedule, and its formal close date now reads as a Sept. 13 backstop. The contract settles when the set does, with the usual review lag after the winning point. If price-as-probability is a new idea, our primer on how prediction markets work covers it, and the guide to betting sports on Kalshi walks through order mechanics.
The Board: Two Contracts, One Frozen Tiebreak
Here is the full market 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 |
The row worth narrating is the gap between the columns. The last trades printed at 36¢ on Birrell and 56¢ on Marcinko, but the resting order book Monday morning brackets both names around 50¢ with an 11-point spread on one side and a 14-point spread on the other. That is what an overnight freeze does to a market: nobody wants to quote a tiebreak tightly while the players sleep, so the book goes wide and the mid drifts to the only defensible number, a coin flip. More than 208,000 contracts changed hands in 24 hours on a market that, in game terms, could have as few as four points of tennis left in it.
The Set That Got Here, And Why The Price Ignores It
The match context is real, so let's state it honestly. Marcinko, a 20-year-old Croatian who was the world's No. 1 junior and won the 2022 Australian Open girls' title, has been the form player: she won her first WTA title in Rabat this May, touched a career-high ranking of No. 45 in July, and took the first set from Birrell 6-3. Birrell, a 28-year-old Australian with a career-high of No. 60 and a win over then-fifth-seed Jessica Pegula at this year's French Open, answered by dragging the second set to 6-6.
Here is the discipline this contract teaches: almost none of that survives contact with a tiebreak at 3-3. Marcinko leading by a set matters enormously for the match, and not at all for this market, because the Set 2 Winner contract pays whoever takes this set, even if she loses the match afterward. If Birrell wins the breaker, her contract pays $1.00 and the third set is somebody else's trade. The gap between their published rankings, Marcinko at No. 53 in early August against Birrell's No. 74 in June, is worth a few cents of edge across a full set; across four points, it is nearly invisible. The market's refusal to show a favorite is not laziness. It is the honest answer, and it is the same lesson every short-fuse Kalshi market teaches, whether the underlying is a tiebreak or a single speech: the contract pays the literal question, not the surrounding story.
A Worked Example: What 55¢ Buys You At 3-3
Now the payoff on those wide quotes. Say you like Birrell to steal the set. Monday morning you cannot buy her at the 50¢ a true coin flip implies; the ask is 55¢. One hundred Yes contracts cost $55 and pay $100 if she wins four tiebreak points before Marcinko does (or two clear at 6-6 and beyond). You are risking $55 to win $45 on an event the frozen scoreboard says is roughly even, which means the spread, not the tennis, is charging you five points of probability for the right to trade a sleeping market. The seller collecting that 55¢ is making the opposite bet with the same handicap in reverse. On a resumed tiebreak that could be over in three minutes, that gap is the whole game, and it is why patient traders quote markets like this rather than cross them. If that habit of hunting prices you disagree with, rather than prices you find interesting, appeals to you, our guide to how to actually win on Kalshi is the longer version.
One legal note before anyone opens an account to trade the resumption: Kalshi is a CFTC-regulated exchange, it's 18+, and it isn't available in every state. 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.
And if pricing four points of somebody else's tiebreak isn't your edge, OddsShopper's free expert picks are a better use of a Monday; that's where handicappers work full games with actual research surface, not frozen coin flips. Our experts' US Open betting picks cover this tournament the conventional way, full matches and real prices.
Frequently Asked Questions
What is the score in Birrell vs Marcinko, and when does the match resume? Play was suspended by rain Sunday night with Marcinko up a set at 6-3, the second set at 6-6, and the tiebreak at 3-3. The suspended first-round matches were added to Monday's US Open schedule, so the tiebreak resumes Monday, Aug. 31.
What are the Kalshi odds for the Birrell vs Marcinko Set 2 Winner market? As of 9:15 a.m. ET Monday, Birrell was quoted 44¢ bid / 55¢ ask and Marcinko 43¢ / 57¢, with last trades at 36¢ and 56¢. Both mids sit at roughly 50%, a coin flip, on a combined 208,566 contracts of 24-hour volume across the two names.
How does the Set 2 Winner contract settle if Birrell wins the set but loses the match? It still pays. Each contract resolves purely on who wins set 2. A Birrell set-two win forces a third set and pays her Yes holders in full regardless of what happens after.
Is Kalshi legal and safe to use? Kalshi is a CFTC-regulated exchange and is 18+, but it isn't available in every state and faces active legal challenges, including New York's July 31 lawsuit. Check your own state's status before trading.
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In Summary
Rain at the US Open turned a routine first-round WTA match into the cleanest demonstration of what a Kalshi price is: Birrell vs Marcinko stopped at 6-6, 3-3 in the second-set tiebreak, and the Set 2 Winner market spent the night quoting both women within a few cents of 50 on more than 208,000 traded contracts. The first set, the rankings, and the form lines all still matter for the match; for this contract, only Monday's tiebreak points do, and there may be as few as four of them. The overnight book settled on the only honest read of a frozen tiebreak, with an 11-cent spread attached: it's a coin flip, and you'll pay for the privilege of disagreeing.
