No. 6 seed Jessica Pegula stunned top-seeded Iga Swiatek in the US Open quarterfinals Wednesday night, punching the fourth ticket for an American into the tournament’s semifinals.

With the win, Pegula advanced to the semifinals of a Grand Slam tournament for the first time in her career. There, she’ll join fellow Americans Emma Navarro, Frances Tiafoe and Taylor Fritz. She’ll face unseeded Karolína Muchová for a berth in the championship match.

Pegula in control from the start

Pegula seized control of the first set in the opening game and didn’t let go. She won the first game on Swiatek’s serve, handing the World No. 1 her first broken serve in 26 games. Swiatek hadn’t previously been broken since her opening-round win over Kamilla Rakhimova.

On Swiatek’s second serve, Pegula did it again. She secured her second break of the opening set to take a 3-0 lead. She maintained control on her own serve and didn’t allow a break en route to the 6-2 win. The set took 36 minutes to complete and saw Swiatek commit 18 unforced errors. When it was done, Pegula took a seat on her bench and gave a subtle fist pump.

Swiatek retreated to the locker room, where she took a lengthy break between sets. When she returned to the court, she had changed from her colorful kit into wearing all white.

Swiatek was first to serve again in the second set. This time she held. But Pegula broke her again on her second serve to take a 2-1 lead. Swiatek returned the break to tie the set at 2-2 before Pegula seized control again with a break to take a 4-3 lead. She forced three break points in the game then drew a standing ovation from her fans in the Arthur Ashe Stadium stands after she forced Swiatek to hit wide to secure the break.

Swiatek did not break back. With the match on her racket leading 5-4, Pegula delivered on her third match point for the biggest win of her career.

‘Finally’ a semifinalist

Pegula had previously reached the quarterfinal round in seven Grand Slam tournaments without advancing. She spoke about her breakthrough with ESPN after Wednesday’s win.

Pegula’s win improved her career record against Swiatek to 6-4 and denied Swiatek a shot at her sixth career Grand Slam championship. Swiatek won the 2022 US Open and is a four-time winner at the French Open. Swiatek entered Wednesday’s match guaranteed to maintain her world No. 1 ranking regardless of the outcome.

Pegula won’t have much time to revel in the upset. She’s scheduled to face Muchová in the semifinals at Arthur Ashe Stadium on Thursday. Navarro — seeded 13th — will take on No. 2 seed Aryna Sabalenka in the other women’s semifinal. Thursday’s winners will advance to Saturday’s championship match.

On the men’s side, Tiafoe and Fritz will face off in a semifinal match on Friday, guaranteeing an American berth in the championship round. No. 1 seed Jannik Sinner was scheduled to take on No. 5 seed Daniil Medvedev in the final quarterfinal match later Wednesday. The winner of that match will advance to take on No. 25 seed Jack Draper in the other men’s semifinal.