PICS: Pegula sends world No. 1 Swiatek out of US Open

Images from the US Open women's singles quarter-finals at Flushing Meadows on Wednesday.

Jessica Pegula of the United States knocked out the world number one Iga Swiatek 6-2, 6-4 to reach her first major semi-final at the US Open on Wednesday.

The sixth seed threw her hands into the air after closing out the biggest win of her career in front of the elated home crowd at Arthur Ashe Stadium in her seventh major quarter-final.

"I've been (to the quarters) so many freaking times - I just kept losing," she said. "Finally I can say semi-finalist."

Swiatek, who withdrew from last month's Canadian Open citing fatigue, appeared out of sorts from the start as she struggled with her serve and helped her opponent with 41 unforced errors.

The Pole had not been broken since the first round of the tournament but dropped serve with a double fault in the opening game and again in the third.

Pegula looked in cruise control in the second set as she broke Swiatek again in the third game but the 2022 champion showed signs of life as she broke back with a forehand winner in the fourth.

Pegula would not let her opponent take the momentum, however, keeping up the pressure from the baseline in a four-deuce game seven, as Swiatek smacked her thigh with frustration after sending a forehand out on break point.

Pegula led 40-0 in the final game but needed the encouragement of the home crowd to get her over the line as Swiatek produced a pair of fine winners to stay in it.

The American was finally able to celebrate when Swiatek sent a shot out on match-point.

"Thank you to the crowd," she said. "You carried me through the last game."

Americans Taylor Fritz and Frances Tiafoe also reached the semi-finals in the men's draw.

Muchova whips Haddad Maia to reach semis

Unseeded Czech Karolina Muchova, in only her sixth tournament back after suffering a wrist injury at the 2023 US Open, beat Brazil's Beatriz Haddad Maia 6-1, 6-4 to reach the semi-finals for a second consecutive year at Flushing Meadows, New York, on Wednesday.

Muchova, who returned to action in June, needed medical treatment on multiple occasions during the second set but held on to dispatch the Brazilian 22nd seed in 85 minutes.

"A little weird match, I have to say," Muchova said in her on-court interview after reaching her fourth career Grand Slam semi-final.

"I had little problems, I wouldn't like to comment on it actually if it's fine. But I'm happy I managed it, to run to the bathroom and back. Sorry if it disturbed anyone, but I had no other choice."

Muchova made a fast start as she grabbed a 4-0 double break lead, held to love and, after Haddad Maia finally got on the board, closed out the opening set on serve.

Haddad Maia improved in the second set but Muchova, who suddenly began grabbing her hip between points, unleashed a backhand winner to break for a 3-2 lead before leaving the court with the physio.

The players exchanged breaks over the next two games before Muchova, after having the physio and doctor at her chair, held to reach 5-3 before taking advantage of new balls and sealing victory on her serve with an ace on her first match point.

"The new balls, it goes faster. You can put more spin so when I heard it was new balls (in the final game) I was actually pretty happy," said world number 52 Muchova after improving to 4-0 in career meetings with Haddad Maia.

"I was trying to put the first serves in. I knew it could make some problems so it was nice in the last game."

Haddad Maia, the first Brazilian woman to make the US Open quarter-finals since Maria Bueno in 1968, also required medical attention late in the match when she appeared to be having difficulty breathing.

Muchova, who has not dropped a set at the year's final Grand Slam, will next face either top seed Iga Swiatek or American sixth seed Jessica Pegula for a place in the final.