Jessica Pegula scripted an astonishing comeback "just in the nick of time" to defeat Karolina Muchova on Thursday at the US Open and reach her first Grand Slam final, where she will take on big-hitting Aryna Sabalenka for the title.

The American world number six Pegula battled back from a set and a break down to record a gutsy 1-6, 6-4, 6-2 victory over her 52nd-ranked opponent from the Czech Republic.

Double Australian Open champion and world number two Sabalenka reached her second successive US Open final by seeing off another American, Emma Navarro, 6-3, 7-6 (7/2).

"I thought I was lucky to still be in it," admitted Pegula.

"She made me look like a beginner, she was destroying me and I was about to burst into tears, but it all came down to small moments. I don't know how I turned that around."

Pegula has now won 15 of 16 matches on the US summer hardcourt swing, which saw a title in Toronto and defeat in the Cincinnati final to Sabalenka.

"It's a chance for revenge, but she'll be tough to beat," said Pegula, who has won just two of seven career meetings against the Belarusian.

Pegula, playing in her first Grand Slam semi-final after six painful quarter-final defeats, looked down and out at one stage on Thursday.

The 30-year-old lost the first set in just 28 minutes, was quickly 2-0 down in the second and had to save break point to avoid slipping 3-0 down.

That was the cue for many spectators to leave the Arthur Ashe Stadium, not wanting to witness a second American defeat in quick succession.

But Pegula dug deep to spark an incredible recovery during a rollercoaster conclusion to a thrilling semi-final as she raced away with eight of the last 10 games.

"I was super-flat, I felt loose but maybe a little too loose," added Pegula.

"But I was able to adapt just in the nick of time and to reach a final is a childhood dream.

"If you'd told me at the start of the year that I'd get to a Grand Slam final I would have laughed so hard at you."

Muchova, a semi-finalist also in 2023 before going on to miss 10 months due to a serious wrist injury, committed her 40th unforced error of the contest on match point, sealing her fate.

"I had a break point for 3-0 in the second set but I missed a volley and everything changed," said Muchova.

"She picked it up and played solid. She was everywhere and played great. All credit to her."

- 'Too late to cheer for me' -

Sabalenka, the runner-up to America's Coco Gauff last year, went through to the final by seeing off Navarro as well as a partisan home crowd.

Navarro, playing in her first semi-final at the majors, went down fighting when she clawed her way back from 3-5 in the second set to force the tiebreak.

Sabalenka cracked 34 winners to the 13 of the 23-year-old American as she moved one win away from a third Grand Slam title.

"Guys, now you're cheering for me. Wow. It's a bit too late," Sabalenka, 26, told the Arthur Ashe Stadium crowd.

"It really means a lot and even though you guys were supporting her still, I had the goose bumps for you cheering. It was an incredible atmosphere."

She added: "I don't really care who I face in the final because today was a good test of the crowd cheering for my opponent. I don't care. I'm ready to face whoever."

Navarro, who had lost in the first round on her two previous appearances at the US Open, admitted that the occasion may have caught her on the hop.

"Maybe I didn't deal with it 100 percent the way I wanted to throughout the match, but it's a feeling that I'll definitely be seeking again," she said.