How a top 11 Polymarket whale turned a tennis underdog into a half‑million‑dollar night

One of the most talked‑about matches of the 2026 US Open also produced one of the cleanest trading signals we’ve seen on Polymarket. At 8:55 PM EDT on Tuesday, more than two hours before Ben Shelton and Carlos Alcaraz walked onto Arthur Ashe Stadium, our alert system flagged an account called beachboy4 buying 679,561 shares of Shelton at 24 cents, a $163,095 bet on the underdog.

The match that followed became a marathon: 4 hours and 28 minutes, finishing at 3:33 a.m., the latest in US Open history. Shelton took the fifth set in a tiebreak, 10–7, and closed it with an ace. At 4:04 a.m., just 31 minutes after match point, the contract redeemed at $1 per share, returning $680,652.79. Profit on the night was $511,099.

Even though that win was large, it was not beachboy4's largest win. beachboy4’s biggest single win is $4.25 million, from two soccer markets that settled on January 18. Ten days later, his biggest loss was $4.21 million on Paris Saint‑Germain, again, soccer. If you stack his four largest wins against his four largest losses, they total $13.7 million and –$14.9 million. All eight were soccer matches played within the same two‑week window in January, and together they left him about $1.2 million poorer. Despite that rough patch, his overall book is up roughly $6.2 million.

The Shelton bet stood out because it broke his recent pattern. Over the past few weeks, he has mostly backed favorites. Since August 20, 26 of his last 29 tickets were bought at roughly coin‑flip odds or better, most between 70 and 89 cents. In that stretch, he staked $3.88 million across 29 markets, won 23 of them, took back $5.40 million, and profited $1.51 million.

His only other cheap shots were two long‑shot underdogs, Christopher O’Connell vs. Taylor Fritz in Cincinnati at 13.8 cents and Jenson Brooksby vs. Jaime Faria at 34.9 cents, and both lost, costing him almost $90,000. Shelton at 24 cents was just his third trade bought so cheaply, and by his own recent track record it looked like it should end poorly too. Instead, it became one of his best nights.

Today, beachboy4 sits 11th all‑time in sports on Polymarket with about $6.2 million in profit. He holds only one open position: a small $10,000 stake on Donald Trump winning the 2028 Republican nomination, bought at 4 cents and now trading near 2, down 50%. This bet cannot settle for another two years. If this prediction proves to be correct, in two years, beachboy4 will take home $250,000, a 25x return. Will he be correct, though? Only time will tell.