NEW YORK — Jessica Pegula could do nothing right as she entered her first Grand Slam semifinal. Her US Open opponent on Thursday night, Karolina Muchova, could do nothing wrong.

“I came out flat, but she played unbelievable,” Pegula said. “She made me look like a beginner. I was about to burst into tears because it was embarrassing. She destroyed me.”

Pegula shook off a slow start and came from a set and a break down to beat Muchova 1-6, 6-4, 6-2 for a place in the final at Flushing Meadows. The sixth-seeded Pegula, a 30-year-old from New York, has won 15 of her last 16 matches and will face No. 2 Aryna Sabalenka for the title on Saturday.

It will be a repeat of last month’s final on the hardcourt of the Cincinnati Open, which Sabalenka won. That is the only blemish on Pegula’s record after the Olympics.

“Hopefully,” Pegula said, “I can get revenge here.”

Pegula’s parents own the Buffalo Bills (NFL) and the Buffalo Sabres (NHL); her father was in the stands at Arthur Ashe Stadium on Thursday, as were her sister, brother and husband.

Things weren’t looking rosy for Pegula on the cool evening.

Muchova, who finished second at Roland Garros in 2023 but was unseeded after being out for about 10 months due to wrist surgery, deployed all her versatility and creativity, qualities that make her so difficult to beat on any surface.

The slices. The touch at the net. The serve-and-volley. Ten of the first 12 winning sets of the match came from her racket. The first set lasted 28 minutes and Muchova won 30 of the 44 points.

“I came out flat, but she played unbelievable. She made me look like a beginner,” Pegula said. “I was about to burst into tears because it was embarrassing. She destroyed me.”

Muchova took eight of the first nine games and was one point away from a 3-0 lead in the second set. But she couldn’t convert a break chance there, she messed up a forehand volley and everything changed.

“I thought, ‘Okay. That was a little bit of luck. You’re still in it,'” Pegula said. “It comes down to really small moments that turn the momentum around.”

Quickly, the 52nd-seeded Muchova went from not being able to miss a shot to not being able to make one. And Pegula turned it on, heeding the advice of her two coaches to mix up her serves and spins and to take Muchova’s backhand.

“She was everywhere,” Muchova said. “She started playing much better.”

Pegula, in particular, demonstrated the confident tennis she used to knock out No. 1 Iga Swiatek, a five-time major champion, in straight sets on Wednesday. Pegula was 0-6 in major quarterfinals before that breakthrough.

It took Pegula a while to get going on Thursday, but once she got going, whoa, she did. All told, she won nine of 11 games, a stretch that not only saw her turn the second set but race to a 3-0 lead in the third.

“I was able to find a way, find some adrenaline, find my legs. And then, at the end of the second set, in the third set, I started playing the way I wanted to play. It took a while,” Pegula said. “I don’t know how I turned that around.”

Muchova, a 28-year-old from the Czech Republic, had not lost a set in the tournament up to that point. But she was starting to fade. After scoring 7 out of 7 in the first set, she went 15 out of 19 the rest of the way. After only seven unforced errors in the first set, she had 33 in the second and third sets.

And meanwhile, the crowd in Arthur Ashe Stadium, which had initially been very quiet (except for the occasional chant of “Come on, Jess!”), was cheering.

“To even make it to the semifinals and feel like my game is there, that I can compete with the best, that I can beat them, that’s something I didn’t know when it would come back, and I feel like I’m playing at a good level,” Muchova said. “I’m healthy and I can play more tournaments this year. That’s actually the most important thing.”

It was the 25th US Open women’s semifinal in the Open era that ended in an opening set of 6-1 or 6-0. Before Thursday, only three women had lost the first set by that score and gone on to win: Sabalenka (2023), Victoria Azarenka (2020) and Svetlana Kuznetsova (2004).

Pegula’s victory means both the men’s and women’s finals will feature an American, the first time that has happened at a major since Wimbledon in 2009. The last time this happened was at the US Open in 2002, when Serena Williams defeated Venus Williams and Pete Sampras defeated Andre Agassi.

ESPN Stats & Information and The Associated Press contributed to this report.