Defending champion Jannik Sinner came through a tough physical battle against Holger Rune to reach the Australian Open quarter-finals.

In a match disrupted by medical timeouts and a broken net, both Sinner and Rune seemed to struggle with the 32C heat on Rod Laver Arena.

Sinner, towards the end of the second set and into the third, was visibly shaking during the changeovers as he wrapped ice towels around his neck.

But the world number one prevailed to win 6-3 3-6 6-3 6-2 against the Dane.

"I was not feeling really well," said Italy's Sinner.

Speaking on court after his win, the 23-year-old said: "I knew in my mind even before the match I would struggle today.

"This morning was a very strange morning because I didn't even warm up today, trying to go on court as fit as I could."

He will face Alex de Minaur, the last Australian standing in the singles, next after he claimed an assured 6-0 7-6 (7-5) 6-3 win over American Alex Michelsen to reach the Melbourne last eight for the first time.

"There's nothing I want more than to play well here in Australia in front of you guys. I'm glad I finally made it to the quarter-finals here but let's go for bigger and better things," said eighth seed De Minaur.

Elsewhere, fellow Italian Lorenzo Sonego beat American qualifier Learner Tien 6-3 6-2 3-6 6-1 to reach his first Grand Slam quarter-final.

Sonego will play 21st seed Ben Shelton next after the American's fourth-round opponent, Frenchman Gael Monfils, retired with a back issue while trailing 7-6 (7-3) 6-7 (3-7) 7-6 (7-2) 1-0.