Sinner toughs it out as Tien hobbles out, Monfils retires at Melbourne Park

MELBOURNE :Jannik Sinner battled through illness to reach the quarter-finals of the Australian Open on Monday as his Italian compatriot Lorenzo Sonego ended teenager Learner Tien's fairytale run.

Madison Keys later turned back the clock to stun Elena Rybakina and Elina Svitolina brought a "little light" to war-torn Ukraine by beating Russian Veronika Kudermetova 6-4 6-1 on another hot day in Melbourne.

The stifling heat did not help defending champion Sinner when he started struggling physically in the second set of his fourth-round match against Dane Holger Rune on Rod Laver Arena.

The top seed did not want to go into detail on what was ailing him but admitted to having dizzy spells before a lengthy medical timeout in the third set that proved a turning point in his 6-3 3-6 6-3 6-2 victory.

"I was not feeling really well," said 23-year-old Sinner, who equalled the Italian record set by Nicky Pietrangeli by reaching his 10th Grand Slam quarter-final.

"I think we saw that today, I was struggling physically. Came here as late as possible. I knew that it was going to be very, very difficult today."

Unseeded Sonego made it two Italians in the quarter-finals when he stopped hobbling 19-year-old American qualifier Tien 6-3 6-2 3-6 6-1, having also taken out Brazilian young gun Joao Fonseca in the second round.

"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."

Tien, who was bidding to become the youngest man to reach the quarters since Goran Ivanisevic did it as a 17-year-old in 1989, stretched his strapped right thigh after a double fault and never looked comfortable physically.

Ivanisev