The World No. 1, despite feeling unwell in sweltering conditions, kept up his title defense with a four-set triumph.

Jannik Sinner has played down an illness which left him “dizzy” and seeking treatment as his Australian Open title defence came under significant threat on Monday.

Jannik Sinner will face his trickiest test yet at the Australian Open when the defending champion battles Dane Holger Rune in the fourth round on Monday, while five-times Grand Slam winner Iga Swiatek will be the heavy favourite against lucky loser Eva Lys.

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.

Jannik Sinner has revealed that he felt unwell ahead of his win over Holger Rune at the Australian Open, and is relieved to be through to the quarter-finals.

Jannik Sinner will face his trickiest test yet at the Australian Open when the defending champion battles Dane Holger Rune in the fourth round on Monday, while five-times Grand Slam winner Iga Swiatek will be the heavy favourite against lucky loser Eva Lys.

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.

Jannik Sinner came through a gruelling match against Holger Rune at the Australian Open, but there were concerns over his health during the clash as he admitted he was not feeling well before the encounter even got underway.