A trader with an 89% hit rate just put $35,127 on a tennis match

Arthur Fils has played Stefanos Tsitsipas five times and won all five. In Miami this spring, he won 6-0, 6-1. Two weeks ago, he beat Frances Tiafoe to take the Cincinnati Open, the first Masters 1000 title of his career. So when the draw put those two men against each other in the first round of the US Open, Fils opened as the clear favorite, and a Polymarket trader called 0b1 spent 18 minutes on Monday morning buying as much of him as the order book would sell.

He finished with 41,948 shares at an average of 83.73 cents. Total cost is $35,126.89, for a profit of $6,821.

Since June, 0b1 has made 2,033 separate purchases, and the middle price he paid was 95.1 cents. Of the $8.9 million he pushed through the book, 83% went in at 90 cents or higher. In July, he spent $399,224 on 400,000 shares of Egypt not winning the World Cup, at 99.8 cents each, to make $776.

This is his style: find the thing that is already true, buy it in absurd size, and collect the last penny nobody else wants.

Fils at 84 cents is the cheapest big bet he has made in months. On August 22, he put $37,600 on Fils against Flavio Cobolli and took $40,000 back. The next day, he paid 70 cents a share for 64,037 shares of Fils in the Cincinnati final and collected $64,037, a profit of $18,596.

Which sounds like a terrible way to make a living, and by the usual arithmetic it is. Buy at 95 cents, and you win a nickel when you are right and lose 95 when you are wrong. At 95 cents, you have to be correct 95 times out of 100 just to finish the year where you started.

But he is up $126,301.37.

Across 192 settled markets since June, he has won 171 and lost 21. That's an 89% hit rate. The question is: will he be right again on this bet specifically?