American Jessica Pegula upset world No. 1 Iga Swiatek 6-2, 6-4 on Wednesday night at the US Open to reach her first Grand Slam semifinal.

The No. 6-seeded Pegula entered the day as the only player inside the WTA’s top 10 who hadn’t reached a major semifinal; she was 0-6 in her career in Slam quarterfinals, one loss shy of the worst major quarterfinal record by any woman in the Open era, shared by three players.

Now she will take on unseeded Karolina Muchova for a spot in Saturday’s final.

Pegula’s win guarantees the US Open will have multiple American men and women playing in the semifinal round; the last time that happened was in 2003 (Andre Agassi and Andy Roddick; Lindsay Davenport and Jennifer Capriati).

Before Pegula, the last American woman to defeat the world No. 1 at any major was Shelby Rogers, who knocked out Ashleigh Barty in the third round of the 2021 US Open.

Swiatek entered the match with Pegula having been broken twice in her first 36 service games through four rounds of the tournament — both breaks coming in her first-round match against Kamilla Rakhimova. On Wednesday night, she was broken four times in eight service games.

Entering Wednesday, Swiatek held a 6-3 edge in her head-to-head matchups with Pegula. Their last meeting was at the WTA Finals in Cancún, where Swiatek defeated Pegula 6-1, 6-0 in the most lopsided championship match in the history of the year-end event.

ESPN Stats & Information contributed to this report.