NEW YORK -- Jessica Pegula pulled off a major upset of Iga Swiatek at the US Open, beating the No. 1-ranked woman 6-2, 6-4 on Wednesday night to win a Grand Slam quarterfinal for the first time on her seventh try.
"There have been so many freaking times, and I just kept losing," Pegula told the crowd. "I know everyone keeps asking me about it, but I was like, 'I don't know what else to do. I just need to get there again and, like, win the match.' So thank God I was able to do it. And finally -- finally! -- I can say, 'Semifinalist.'"
Her win guarantees the US Open will feature multiple American men and women in the semifinal round, the first time that has happened since 2003 (Andre Agassi and Andy Roddick; Lindsay Davenport and Jennifer Capriati).
The No. 6-seeded Pegula, a 30-year-old American, has won 14 of her past 15 matches and will make her debut appearance in the semifinals of a Slam on Thursday against unseeded Karolina Muchova of the Czech Republic.
Both Muchova and Pegula have yet to drop a set, the first time that has been done by multiple women at this stage of the tournament since 2014 (there were three that year: Serena Williams, Peng Shuai and Ekaterina Makarova).
"I know she has a lot of experience going deep in Slams," Pegula said about Muchova, whom she defeated at the Cincinnati Open last month. "I'll worry about that, maybe, when I wake up in the morning."
The other women's match Thursday also will feature an American making her major semifinal debut, No. 13 Emma Navarro, against No. 2 Aryna Sabalenka, who has won the past two Australian Open titles. Sabalenka lost to Coco Gauff in the 2023 final in New York; Navarro ended Gauff's title defense in the fourth round.
There are also two Americans in the men's semifinals, but they'll face each other: No. 12 Taylor Fritz takes on No. 20 Frances Tiafoe on Friday.
The lopsided nature of Pegula's win was surprising, but she believed this day would come.
"I knew I could do it. I just had to go out and execute my game and not get frustrated," she said. "Luckily I felt like I was able to take advantage of some things she wasn't doing well very early and then was able to kind of ride that momentum throughout the match."
Swiatek served poorly in the first set and her forehand was a real problem, with 22 of her 41 unforced errors coming on that side. Pegula made only 22 unforced errors in all and used terrific defense to keep forcing Swiatek to hit an extra shot.
Pegula repeatedly did what seemed nearly impossible lately against Swiatek, who counts the 2022 US Open among her five Grand Slam titles and has led the WTA rankings for most of the past 2½ years: break her serve.
Entering Wednesday, Swiatek had lost only a pair of service games across four matches in the tournament, both in the first round -- and she didn't even face a single break point in any of her most recent three contests.
But Pegula, whose parents own the NFL's Buffalo Bills and NHL's Buffalo Sabres, didn't have much trouble in that department, especially at the outset, breaking in each of Swiatek's initial two service games, which both ended with double-faults, and three of the first six.
It helped that Swiatek was unable to properly calibrate her first serves early, putting just 2 of 12 -- 16.7% -- in play at the start and only 36% for the opening set.
Even as the games kept going in her favor, Pegula didn't show much perceptible emotion, whether grabbing a 4-0 lead just 21 minutes in or taking up that set, which was greeted with a slight shake of her left fist as she walked to her sideline seat.
Swiatek didn't hide her thoughts that well. She smacked her racket against the top of the net. She slapped her right thigh after a forehand flew wide to get broken yet again and trail 4-3 in the second set. Fifteen minutes later, it was over.
"It's never easy to play against Jess," Swiatek said. "She has a tricky ball because it's pretty low and pretty flat. I just made too many mistakes."
Pegula entered the day as the only player inside the WTA's top 10 who hadn't reached a major semifinal; 0-6 in her career in Slam quarterfinals, she was one loss shy of the worst major quarterfinal record by any woman in the Open era, shared by three players (0-7).
During that 0-6 rut, two of her exits came against Swiatek, and one was against another No. 1 player, Ash Barty.
Pegula was asked about that record in this round during her postmatch interview on court after winning her fourth-round match. And again in the news conference that followed. And again during a TV interview before stepping out into Arthur Ashe Stadium on Wednesday.
If that all weighed on Pegula, she didn't let it show.
ESPN Stats & Information and The Associated Press contributed to this report.