NEW YORK — Jessica Pegula could do no right at the outset of her first Grand Slam semifinal. Her opponent at the US Open on Thursday night, Karolina Muchova, could do no wrong.

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

Pegula managed to shrug off that sluggish start and come back from a set and a break down to defeat Muchova 1-6, 6-4, 6-2 for a berth in the final at Flushing Meadows. The No. 6-seeded Pegula, a 30-year-old from New York, has won 15 of her past 16 matches and will meet No. 2 Aryna Sabalenka for the title on Saturday.

It will be a rematch of last month’s final at the hard-court Cincinnati Open, which Sabalenka won — the only blemish on Pegula’s post-Olympics record.

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

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

Things did not look promising for Pegula early on the cool evening.

Muchova, the 2023 French Open runner-up but unseeded after missing about 10 months because of wrist surgery, employed every ounce of her versatility and creativity, the traits that make her so hard to deal with on any surface.

The slices. The touch at the net. The serve-and-volleying. Ten of the match’s first 12 winners came off her racket. The first set lasted 28 minutes, and Muchova won 30 of its 44 points.

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

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

“I was thinking, ‘All right. That was kind of lucky. You’re still in this,'” Pegula said. “It comes down to really small moments that flip momentum.”

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

“She was everywhere,” Muchova said. “She started to play way better.”

Most of all, Pegula demonstrated the confident brand of tennis she used to eliminate No. 1 Iga Swiatek, a five-time major champion, in straight sets Wednesday. Pegula had been 0-6 in major quarterfinals before that breakthrough.

Took Pegula a while to play that well Thursday, but once she got going, whoa, did she ever. All told, she collected nine of 11 games, a span that allowed her to not merely flip the second set but race to a 3-0 edge 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, into the third set, I started to play like how 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, hadn’t ceded a set in the tournament until then. But she began to fade. After going 7-for-7 on points at the net in the first set, she went 15-for-19 the rest of the way. After only seven unforced errors in the first set, she had 33 across the second and third.

And all the while, the Arthur Ashe Stadium crowd that was flat at the beginning — save for the occasional cry of “Come on, Jess!” — was roaring.

“To even get to the semis and to feel that my game is there, that I can compete against the best, I can win against them, it’s something that I didn’t know when it will come back to me, and I feel I’m playing 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 to feature a 6-1 or 6-0 opening set; before Thursday, only three women had come back to win after dropping the first set by that score — Sabalenka (2023), Victoria Azarenka (2020) and Svetlana Kuznetsova (2004).

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

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