MELBOURNE, Australia -- Iga Swiatek took three hours in the afternoon heat to beat 36-year-old Kaia Kanepi 4-6, 7-6 (2), 6-3 on Wednesday, with the payoff being a spot in the Australian Open semifinals against Danielle Collins.
"This match was crazy,'' said the 20-year-old 2020 French Open winner. "First set I think my mistake was I had so many break points, I felt like I missed my chances. In the second set, I felt like she's playing so fast that I can't be tight. I had to finish my forehands.''
The temperature hit 97 degrees Fahrenheit on Day 10, continuing a week of hot days at the year's first Grand Slam tournament.
Collins won the opening match on Rod Laver Arena before the heat peaked, swinging it in her favor with a key service break in the final game of the opening set on her way to a 7-5, 6-1 victory over Alize Cornet.
No. 115-ranked Kanepi made her Grand Slam debut in 2006 but was playing in the quarterfinals in Australia for the first time, completing a career set after making it to the last eight twice at each of the sport's three other major tournaments.
She was coming off an upset, three-set win over No. 2-ranked Aryna Sabalenka and took the game to Swiatek, who saved nine set points before losing the first set.
Swiatek rallied in the second, exchanging service breaks twice before winning it in a tiebreaker.
There was another exchange of breaks early in the third set, and Swiatek was broken again when she was serving for the match in the eighth game. She eventually clinched on Kanepi's serve, scrambling to stay in the point until the Estonian player sent a forehand wide.
As she left the court, Swiatek wrote on the TV camera lens: "Thank you for the support. #Tired.''
Collins' win means there are two Americans in the last four. Keys, the 2017 US Open runner-up, will play reigning Wimbledon and 2019 French Open winner Barty.
Swiatek of Poland is the only one of the four in the Australian Open semifinals for the first time. Collins lost to Petra Kvitova in the 2019 semifinals in Australia, which remains her best run to date at a major. Keys lost to Serena Williams in 2015, and Barty lost a semifinal in 2020 to eventual champion Sofia Kenin.
Collins underwent surgery last year to treat endometriosis, a condition that had caused her severe pain during tournaments in 2021.
"It feels incredible, especially after some of the health challenges I've had,'' Collins said in her postmatch interview. "To be able to get back to this level and be able to compete like the way I have been and being able to be as physical as I haven't been so rewarding.
"I feel pretty good right now. I've had some great matches along the way at this tournament ... really happy about how I'm feeling physically and mentally.''
For Cornet, the loss ended a career-best run. The quarterfinal was her first in 63 Grand Slam main draw appearances. The WTA predicts that the 32-year-old Cornet should return to the top 50.
Cornet had anticipated an aggressive game strategy from Collins, but the power in the ground strokes was "even more than what I expected.''
"I felt out of breath all the time. I couldn't, like, play my game," Cornet said. "She just never let me do it, never gave me the time.''
The Associated Press contributed to this report.