Jannik Sinner gets past Holger Rune at the Australian Open in a match with net and medical delays

First came the medical timeouts, one each for Jannik Sinner and Holger Rune with the temperature above 90 degrees Fahrenheit (32 Celsius) at the Australian Open.

Then came the bizarre sight of a 20-minute delay because the net at Rod Laver Arena detached from the court after being hit by a big Sinner serve.

In the end, the breaks in action were "lucky," Sinner said, because they gave him a chance to catch his breath, put his struggles aside and emerge with the victory - as he keeps doing, no matter the site or the circumstances. The defending champion moved into the quarterfinals at Melbourne Park on Monday by eliminating the 13th-seeded Rune 6-3, 3-6, 6-3, 6-2.

"I don't want to talk so much (about) how I felt today. I was not feeling really well. I think we saw that today. I was struggling physically," Sinner said, declining to say exactly what was wrong. "Playing against a tough opponent, but also playing against myself a little bit."

The No. 1-ranked Sinner occasionally tried to cool off by pressing a cold towel to his face or pouring water down the back of his neck. He was far better down the stretch, both after a 10-minute-plus delay in the third set when he went to the locker room for medical attention and after a 20-minute holdup in the fourth when the screw connecting the net to the blue playing surface came undone.

"It was a bit helpful. I at least felt slightly better when I went back on court," Sinner said about seeing a doctor. "I felt like the face looked a little bit better, the color was a little bit back."

He's won 18 consecutive tour-level matches, dating back to late 2024. Last season, Sinner went 73-6 with eight titles, the first man with that many tournament championships in a single year since Andy Murray in 2016.

That haul included Sinner's first two Grand Slam trophies, at the Australian Open in January and the U.S. Open in September, the latter shortly after he was exonerated for testing positive for an anabolic steroid twice in March. His case is still unresolved, though, with a hearing scheduled for April in the World Anti-Doping Agency's appeal of the ruling.

In the women's fourth round, 2017 U.S. Open runner-up Madison Keys eliminated 2022 Wimbledon champion Elena Rybakina 6-3, 1-6, 6-3, and now plays Elina Svitolina, a 6-4, 6-1 winner against Veronika Kudermetova. Five-time major champion Iga Swiatek had - no surprise here - an easy time beating "lucky loser" Eva Lys 6-1, 6-0 in just 59 minutes.

Swiatek, who will face No. 8 Emma Navarro next, compiled a 28-7 edge in winners and has ceded a grand total of 11 games through four matches in the tournament. Contrast that to Navarro's path: Her 6-4, 5-7, 7-5 win against No. 9 Daria Kasatkina was the American's fourth three-setter in four matches in Melbourne, and she has dropped more than 60 games while spending more than 10 hours on court.

Sinner will play No. 8 Alex de Minaur of Australia, who defeated unseeded Alex Michelsen of the U.S. 6-0, 7-6 (5), 6-3 at night to reach the quarterfinals at his home Grand Slam tournament for the first time. A second Italian joined Sinner in the quarterfinals when 55th-ranked Lorenzo Sonego got that far at a major tournament for the first time by ending the run of American qualifier Learner Tien 6-2, 6-3, 3-6, 6-1.

Sonego will go up against No. 21 Ben Shelton, who advanced when 38-year-old Gael Monfils of France quit because of an injury early in the fourth set. The 22-year-old American was leading 7-6 (3), 6-7 (3), 7-6 (2), 1-0 after nearly three hours when Monfils, who is married to Svitolina, called a halt to the match.

The men's quarterfinals Tuesday will be Novak Djokovic vs. Carlos Alcaraz, and Alexander Zverev vs. Tommy Paul.

Sinner said he showed up late at Melbourne Park and didn't hit before his match because he wasn't feeling great. The first obvious signs of trouble came at 3-all in the second set.

After lunging for a shot behind the baseline and stumbling slightly, Sinner clutched at his upper left leg and looked as though he might be bothered by some sort of discomfort, although it wasn't entirely clear what was going on.

After Rune held there, Sinner walked slowly to the sideline for the ensuing changeover and was breathing heavily during the time between games.

When play resumed, Rune earned his first break point of the match, and Sinner handed it over with a double-fault that made his deficit 5-3.

It was a muggy afternoon, and long, physical points left both players spent. After a pivotal, 37-stroke exchange in the third - claimed by Sinner with a cross-court swinging forehand volley passing winner after bringing Rune forward with a drop shot - each man leaned over with hands on his knees, gasping for air.

Then, during the changeover at 3-2 in the third set, Sinner asked for a trainer, and told a ball kid to bring him something to drink from his team. Sinner's pulse was checked, and then he trudged off with a towel draped around his neck and a bottle in each hand.

When action resumed, Rune was the one playing a bit recklessly and without an effective game plan, and he got broken to trail 5-3 - then immediately requested his own medical check, during which his right knee was massaged by a trainer.

"It was, for sure," Sinner said, "very, very tough."