World No. 1 Jannik Sinner fought through blistering heat and an undisclosed ailment to defeat Holger Rune 6-3, 3-6, 6-3, 6-2 and advance to the quarterfinals of the Australian Open on Monday.

Sinner, the defending champion, met with the tournament doctor before beginning the match and needed a medical timeout in the third set.

“I think we saw that today I was struggling physically,” the Italian said after the match. “Came here as late as possible. I knew that it was going to be very, very difficult today. You know, playing against a tough opponent, but also playing against myself a little bit.”

The match, played in 90 degrees and humid conditions in Melbourne, Australia, also featured a 21-minute delay that gave players an indoor break as officials repaired a broken ring that keeps the net in place.

Rune, the No. 13 seed, also required his own medical timeout to give a trainer a chance to massage his right knee. The Dane’s break gave Sinner an additional chance to rest in the match, which lasted just over three hours.

Sinner tallied 14 aces among his 35 winners, which accompanied 35 unforced errors, and won 83 percent of his first-serve points. Rune wound up with 54 unforced errors against 31 winners.

In the quarterfinals, Sinner will face No. 8 Alex de Minaur of Australia, who ousted American Alex Michelsen 6-0, 7-6 (5), 6-3. It will be the first quarterfinals appearance for de Minaur in his home country’s Grand Slam, and he became just the third Aussie man to reach the round in 20 years.

“It means the world,” de Minaur said. “There is nothing I want to do more than play well here in Australia in front of you guys. I am glad I finally made it to the quarterfinals. Let’s go for bigger and better things.”

Ben Shelton will be making his second appearance in the Australian Open quarterfinals after 38-year-old Gael Monfils of France was forced to retire due to a back injury, with Shelton up 7-6 (3), 6-7 (3), 7-6 (2), 1-0 after two hours, 56 minutes.

The magical run for another American, 19-year-old qualifier Learner Tien, ended with a 6-3, 6-2, 3-6, 6-1 loss to Italian Lorenzo Sonego, who will meet Shelton in the quarterfinals. Tien, who struggled physically in the match, defeated World No. 5 Daniil Medvedev of Russia in a five-set thriller in the second round.

–Field Level Media