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 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 either Australian eighth seed Alex de Minaur or American Alex Michelsen in the last eight.

Elsewhere, Italy's 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.

After two gruelling service games in the third set, Sinner's physical troubles came to the fore and he called for the trainer after saving a break point to go 3-2 up.

He received treatment off-court and returned after more than 11 minutes, but it was Rune who faltered and allowed Sinner to break for a 5-3 lead.

The 13th seed needed a medical timeout of his own for an apparent knee injury before Sinner raced to a love hold to wrap up the set.

There was a further 21-minute pause in play at the start of the fourth as the pair returned to the locker room when the net's anchoring pin in the middle came loose.

The interval seemed to benefit Sinner, who steamrolled his way to a 5-2 lead and served out the victory after three hours and 13 minutes.

"It was very tough. I knew in my mind he had some very long matches so I tried to stay there mentally," Sinner added.

"Today the support meant so much to me, I really needed you guys today. It's 90% yours and 10% I try to make you happy."

Sinner is on a 17-match winning streak, with his last defeat coming in the Beijing Open final against Carlos Alcaraz in October.

There is potential for an all-Italian semi-final tie after unseeded Sonego's win over 19-year-old Tien in four sets.

Tien was bidding to become the youngest man to reach the last eight in Melbourne since a 17-year-old Goran Ivanisevic in 1989 but, with strapping on his right thigh, struggled with injury.

"Today was so tough, I'm so sad that he had a problem. It's not the right way to win, but I'm so happy to reach the quarter-finals," said 29-year-old Sonego.