NEW YORK — Karolina Muchova is back in the US Open semifinals for the second straight year, fighting through a stomach bug and punctuating her return from wrist surgery by beating No. 22 Beatriz Haddad Maia 6-1, 6-4 on Wednesday.

Muchova lost to eventual champion Coco Gauff in the 2023 semis in Flushing Meadows, then missed nearly 10 months because of a wrist injury she suffered during the tournament.

The Czech returned to action in June just before Wimbledon, and a little more than two months later she is into her fourth career Grand Slam semifinal.

“Game-wise, I think every match here I feel better on court and that for sure helps,” Muchova said. “More matches and getting through that experience on the court again, that helps a lot as well to be more confident and feel my shots.”

Muchova will face top-seeded Iga Swiatek or No. 6 Jessica Pegula on Thursday in the semifinals. Australian Open champion Aryna Sabalenka, the No. 2 seed, faces first-time Grand Slam semifinalist Emma Navarro in the other semi.

Muchova dominated the first set, racing to a 5-0 lead and finishing it off in 35 minutes. Then it became a test in the second, with both players struggling physically on a sunny afternoon.

Muchova left the court at one point for what she said was a needed trip to the bathroom, while Haddad Maia appeared to be pointing to her chest and trying to breathe deeply midway through the set before burying her head in a towel as trainers attended to her.

“I’m fighting bug a little bit. I’m a little sick,” Muchova said in her postmatch news conference. “I hope (the bathroom break) didn’t disturb her, didn’t disturb the people.”

Muchova has had to get used to dealing with pain.

She had just made her second major semifinal of 2023, having lost to Swiatek in the French Open final, when she had to stop playing following the US Open. When she finally got back to the tour this year, it left time for only 11 matches before returning to Flushing Meadows.

That was enough time for Muchova to rediscover her game. She hasn’t dropped a set in her five matches and finished off this one with an ace down the middle. She is the 19th unseeded woman in the Open era to reach the semifinals in New York, and only the fifth to do so without a dropping a set, alongside Mima Jausovec (1976), Flavia Pennetta (2013), Peng Shuai (2014) and qualifier Emma Raducanu, who won the title in 2021.

Muchova, who missed most of the first half of the 2022 season because of back, abdominal and ankle problems, said she didn’t like to talk about her injuries.

“I’ve been through a lot of them,” the 28-year-old said. “Yeah, this last one, the wrist surgery, was one of the worst ones that I had. Now looking back, I’m, like, ‘Oh, it actually flew by, the time, and I feel strong again.’

“But when I go back to February, I have to say I wasn’t always that positive. It was tough moments, honestly, when I couldn’t move the arm and couldn’t do much.”

Muchova noted she is now pain-free and feels fit “besides that I’m a little bit sick — but the body is fine.”

Many fans hadn’t even taken their seats at Arthur Ashe Stadium when Muchova broke Haddad Maia in a 14-point game to take a 2-0 lead. The Brazilian faced that same deficit in her third-round match against Anna Kalinskaya but won the next game to start a turnaround, helped in part by a video review that gave her a point.

The U.S. Tennis Association acknowledged the next day that Haddad Maia’s shot was illegal, but the chair umpire wasn’t given the relevant replay that would have shown that.

Muchova wouldn’t allow a turnaround this time, denying Haddad Maia — the first Brazilian woman to make the US Open quarterfinals since Maria Bueno in 1968 — what would have been the second major semifinal of her career. She got to that stage in the French Open last year, but said she had trouble concentrating Wednesday.

“I didn’t put pressure on me because of her. It was me and myself, it was my ghosts inside my mind and I know all the tennis players have that,” Haddad Maia said. “Today was like an inner fight. I couldn’t manage that.”

Haddad Maia confirmed she was having some trouble with her chest during the match but is “feeling okay.”

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