Iga Swiatek of Poland waves after defeating Eva Lys of Germany in their fourth-round match at the Australian Open tennis championship in Melbourne, Australia. (AP)

MELBOURNE, Jan 20, (Xinhua): Defending men's champion Jannik Sinner and women's second seed Iga Swiatek had contrasting fourth-round victories on Monday as several players wilted under searing conditions at the Australian Open.

Australia's title hope Alex de Minaur also progressed, but former Wimbledon champion Elena Rybakina crashed out.

In hot and sunny conditions on Rod Laver Arena, top seed Sinner overcame adversity to battle past gutsy 13th seed Holger Rune.

Having dropped the second set, an ailing Sinner's title defense appeared to be hanging by a thread when he required medical treatment in the third set.

Sinner looked exhausted and was visibly shaking before he won 6-3, 3-6, 6-3, 6-2 in a see-sawing match lasting three hours and 13 minutes.

The two-time Grand Slam champion will next play de Minaur, who beat 20-year-old Alex Michelsen 6-0, 7-6 (5), 6-3.

"It was very, very tough. I knew he had some tough matches and I tried to stay connected with my serving and returning game," Sinner said.

Veteran Lorenzo Sonego reached his first Grand Slam quarterfinal after beating 19-year-old qualifier Learner Tien 6-3, 6-2, 3-6, 6-2.

The 29-year-old was unstoppable on serve and handled the stifling conditions better than Tien, whose breakout tournament was highlighted by an upset of fifth seed Daniil Medvedev in round two.

Sonego will next play 21st seed Ben Shelton, who progressed after 38-year-old Gael Monfils pulled the pin as his grueling run finally took its toll.

Shelton led 7-6 (3), 6-7 (3), 7-6 (2), 1-0 after almost three hours as Monfils succumbed having in his previous match impressively defeated fourth seed Taylor Fritz in four sets.

But it was better news for 28th seed Elina Svitolina, Monfils' wife, who was the first women's player through to the last eight.

She overcame a slow start to power past Russia's Veronika Kudermetova 6-4, 6-1 in one hour and 23 minutes.

It's been a resurgence for former world No.3 Svitolina, who reached the quarterfinals in Melbourne for a third time but first since 2019.

"I was just trying to fight," said the 30-year-old Svitolina. "The only thing I can do when things are not going your way, you just try to really put your head down and get back to work." Svitolina next plays 19th seed Madison Keys, who beat Rybakina 6-3,1-6, 6-3 in a nerve-jangling clash on Margaret Court Arena.