MELBOURNE, Australia — Stefanos Tsitsipas maintained his perfect record in Grand Slam quarterfinals, beating No. 11-seeded Jannik Sinner 6-3, 6-4, 6-2 Wednesday to reach the last four of the Australian Open.

The 23-year-old, No. 4-ranked Tsitsipas improved to 5-0 at this stage of a major. It’s the semifinals he’s yet to master, winning just one — at Roland Garros last year — from four so far.

He’ll next player either Daniil Medvedev, who made his Grand Slam breakthrough when he won last year’s U.S. Open title, or No. 9 Felix Auger-Aliassime. No. 2 Medvedev and Auger-Aliassime were meeting later Wednesday in a night match.

Tsitsipas didn’t face a break point and converted all four he got on Sinner’s serve in the match that lasted just over two hours, considerably less than his five-set fourth-round win over Taylor Fritz.

The only real delay came from a weather disruption, when a late afternoon storm meant the roof over Rod Laver Arena had to be closed when the Greek star was already up a set and a break.

“I knew I was heading toward the right direction,” Tsitsipas said. “The conditions might have changed a little bit after the roof was closed — slightly faster, not as bouncy as before. I tried to adapt to the new conditions, and it just worked.”

Dozens of ball kids and staff used towels to soak up water on the court in the 15-minute break.

The temperature dropped from the highs of the afternoon, when Iga Swiatek took three hours in the afternoon heat to beat 36-year-old Kaia Kanepi 4-6, 7-6 (2), 6-3, with the payoff being a spot in the semifinals against Danielle Collins.

“This match was crazy,” the 20-year-old, 2020 French Open winner said. “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 reached 36 degrees Celsius (97 degrees Fahrenheit) on Day 10, continuing a week of hot weather.

Collins won the opening match 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 was coming off an upset, three-set win over No. 2-ranked Aryna Sabalenka and took the match 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.

After getting on top in the the third, Swiatek was broken in the eighth game when she was serving for the match. She eventually clinched on Kanepi’s serve, scrambling to stay in the last point until the Estonian player sent a forehand wide.

After the first three quarterfinals were decided in straight sets — Ash Barty beat Jessica Pegula and Madison Keys beat Barbora Krejcikova on Tuesday — the last one went all the way.

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 U.S. Open runner-up, will play reigning Wimbledon and 2019 French Open winner Barty.

Swiatek is the only one of the four players in the Australian Open semis for the first time. Collins lost to Petra Kvitova in the semifinals here in 2019, which remains her best run to date. Keys lost to Serena Williams in 2015 and Barty lost a semifinal final in 2020 to eventual champion Sofia Kenin.

Collins underwent surgery last year to treat endometriosis, a condition which had caused her severe pain during tournaments in 2021.

“It feels incredible, especially after some of the health challenges I’ve had,” Collins said. “To be able to get back to this level and be able to compete like the way I have been … is so rewarding.

“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.”