Jessica Pegula faced a barrage of questions: Why had she been 0-6 in Grand Slam quarterfinals before her U.S. Open clash with top seed Iga Swiatek? What strategies could she employ to alter that record?

These inquiries arose during her on-court interview following her previous victory, continued at the subsequent news conference, and were reiterated in a brief television interview just before she stepped onto the court at Arthur Ashe Stadium on Wednesday night.

Despite the pressure, the 30-year-old American managed to conceal any stress, achieving a significant upset by defeating Swiatek 6-2, 6-4 at Flushing Meadows, thus securing her first semifinal appearance in a major tournament.

“There have been so many times, and I just kept losing,” Pegula remarked, reflecting on her recent form of winning 14 out of her last 15 matches, all on hard courts. “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.’”

She is set to compete against unseeded Karolina Muchova from the Czech Republic on Thursday for a chance to reach the final.

Muchova, who was the runner-up to Swiatek at the 2023 French Open, has reached the semifinals in New York for the second consecutive year, having defeated No. 22 seed Beatriz Haddad Maia 6-1, 6-4 earlier on Wednesday. After losing to Coco Gauff in last year’s semifinals, Muchova underwent surgery on her right wrist and was sidelined from the tour for nearly 10 months before returning in June.

This was just one of several injuries for Muchova, who described it as “one of the worst ones that I had.”

“Doesn’t seem to matter how many matches she’s really gotten in; she seems to have good results no matter what. It’s cool to kind of see her back, because I think she’s really great for the game and the way she plays is really fun,” said Pegula, the No. 6 seed, who previously defeated Muchova at the Cincinnati Open last month. “She’s good, so talented, so skilled as a tennis player. Like, so complete.”

The women's match on Thursday night will showcase an American making her major semifinal debut, No. 13 Emma Navarro, who will compete against No. 2 Aryna Sabalenka, the reigning champion of the last two Australian Open tournaments. Sabalenka faced Gauff in the 2023 final in New York, while Navarro ended Gauff’s title defense in the fourth round.

In the men’s semifinals, two Americans will also go head-to-head: No. 12 Taylor Fritz will take on No. 20 Frances Tiafoe on Friday.

This marks the first occurrence since the 2003 U.S. Open that multiple Americans have advanced to the semifinals in both the women’s and men’s categories.

The other men’s semifinal features No. 1 Jannik Sinner against No. 25 Jack Draper. Sinner secured his spot in the final four at Flushing Meadows for the first time by defeating 2021 champion Daniil Medvedev with a score of 6-2, 1-6, 6-1, 6-4 on Wednesday night. Draper advanced by eliminating Alex de Minaur in straight sets.

Pegula’s decisive victory was unexpected, yet she remained confident that this moment would come. “I knew I could do it,” she stated. “I just had to go out and execute my game and not get frustrated.”

Swiatek struggled with her serve in the first set, and her forehand was particularly problematic, contributing to 22 of her 41 unforced errors. In contrast, Pegula recorded only 22 unforced errors overall and showcased excellent defensive skills, compelling Swiatek to hit additional shots.

“It’s never easy to play against Jess. She has a tricky ball because it’s pretty low and pretty flat,” Swiatek remarked. “I just made too many mistakes.”

Pegula consistently broke Swiatek’s serve, despite Swiatek being a five-time Grand Slam champion and having held the WTA rankings for the majority of the past 2.5 years, including her victory at the 2022 U.S. Open.

Prior to Wednesday’s match, Swiatek had lost only two service games throughout the tournament, both in the first round, and had not faced a single break point in her last three matches. This performance contributed to her being listed as a -350 money-line favorite against Pegula by BetMGM Sportsbook.

Pegula, whose parents own the NFL’s Buffalo Bills and NHL’s Buffalo Sabres, faced little difficulty in her match, particularly at the beginning. She capitalized on Swiatek’s early struggles, breaking her serve in both of Swiatek’s first two service games, which were marred by double-faults, and securing three breaks out of the first six games played.

Swiatek’s inability to find her rhythm with her first serves contributed to the situation, as she managed to land only 2 out of 12 serves—16.7%—in play at the start, and only 36% throughout the first set.

“I didn’t really understand why my serve wasn’t working,” Swiatek remarked.

Despite her early success, Pegula maintained a composed demeanor, whether she was establishing a 4-0 lead just 21 minutes into the match or closing out the first set, which she celebrated with a subtle fist pump as she made her way to her bench.

In contrast, Swiatek’s frustration was evident. She struck her racket against the top of the net and slapped her thigh in exasperation after a forehand went wide, resulting in another break and a 4-3 deficit in the second set.

Fifteen minutes later, the match concluded.

“I feel like when I have high expectations, I never perform well,” Swiatek expressed. “(But) it’s hard to have low expectations when everybody is expecting something from you.”