Australian Open: Sinner needs ‘big luck’ to beat Rune while Swiatek sweeps aside Lys

Defending champion struggles in sweltering Melbourne heat while Pole wins in under an hour

Jannik Sinner has a medical timeout during his win over Holger Rune at the Australian Open. AFP

A smashed net became an unlikely ally of defending champion Jannik Sinner during a sweltering day's action at the Australian Open.

World No 1 Sinner and fourth-round opponent Holger Rune were visibly struggling with the humid conditions on Rod Laver Arena during a match disrupted by medical timeouts for both players on Monday.

The Italian was visibly shaking in the second and third sets as he sat slumped with ice towels around his neck during the changeovers.

“I knew in my mind even before the match I would struggle today,” said Sinner, who eventually came out on top 6-3, 3-6, 6-3, 6-2 against the 13th seed.

“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.

“Game-wise I played well, I served well. The time off the court, me and the doctor, we talked a little bit, it helped me today.”

He refused to say exactly what was wrong with him, only that he was “not there health-wise” and had been “a bit dizzy at times”.

There was also a 21-minute delay when Sinner smashed the metal brace that secures the net to the floor with a thunderous serve early in set four.

That time back in the air-conditioned locker room came as a welcome relief for the 23-year-old, who beat Daniil Medvedev in last year's final to win his first Grand Slam title.

“I was lucky today that … 20 minutes off court, you know, trying to get back physically, putting some cold water in my head, it was very helpful,” Sinner added. “It was big, big luck to me today.”

Rune, who played five, four and five sets in his first three matches, admitted he was also being stretched to his limits physically in the stifling Melbourne heat.

“It was really, really tough,” said Rune, who also needed medical treatment on a sore knee. “I mean, I was almost dying, also. It was really a struggle. I could see he was also struggling.”

Next up for Sinner – who is now on a 17-match win streak – will face Australian eighth seed Alex de Minaur after the home hope defeated Alex Michelsen 6-0, 7-6, 6-3.

American teenage qualifier Learner Tien's fairy-tale run is over after he suffered a thigh problem in a 6-3, 6-2, 3-6, 6-1 defeat to Italy's Lorenzo Sonego.

Tien, who defeated fifth seed Medvedev on his run to a Grand Slam-best fourth-round appearance, had strapping around his right thigh which clearly hampered his efforts.

“I'm so sad that he had a problem,” said the 29-year-old Sonego, who has never previously gone so deep at a Grand Slam.

“It's not the right way to win, but I'm so happy to reach the quarter-finals.”

The Italian will now take on American 21st seed Ben Shelton whose match against Gael Monfils ended with the French veteran retiring in the fourth set.

The 22-year-old won 7-6, 6-7, 7-6, 1-0 with each of the first three sets lasting almost an hour.

“At 38 I hope I'm still walking without crutches,” Shelton said of Monfils. “To push me the way he did the way he did today and entertain everyone is so impressive.”

In the women's draw, world No 2 Iga Swiatek produced another ruthless display at Melbourne Park.

After thrashing former US Open winner Emma Raducanu in the previous round, Swiatek made short work of lucky loser Eva Lys, beating the German 6-0, 6-1 in 59 minutes.

The five-time Grand Slam champion has yet to drop a set and the first-set bagel was her third of the tournament.

“Usually I don't feel comfortable with my game at the Australian Open, but this year it is a bit better,” said the Pole, who has never been beyond the semi-finals Down Under.

“I'm just enjoying being on the court and off the court as well because I definitely have a good time here. Hopefully it's going to last even longer.”

Swiatek will now face American eighth seed Emma Navarro - who defeated Russia's Daria Kastakina 6-4, 5-7, 7-5 - in the quarter-finals.

American Madison Keys upset sixth seed Elena Rybakina 6-3, 1-6, 6-3 in a roller-coaster match on Margaret Court Arena.

Rybakina seemed to be struggling with a lower back injury that had affected her in the third round and 19th-seed Keys was able to play aggressively to neutralise her big serve and take control of the rallies.

Keys will play Ukraine's Elina Svitolina, who beat Veronika Kudermetova 6-4 6-1 earlier on Monday, for a place in the last four.