As home hope Alex de Minaur breezed through in the cool of the night session to set up a bumper quarter-final with Sinner, the top seed had to battle tooth and nail to keep his title defence alive.

After waking up unwell and forgoing his usual pre-match warm-up, Sinner eventually triumphed 6-3 3-6 6-3 6-2 to book a quarter-final against Australian No.1 Alex de Minaur.

The eighth-seeded Australian ended Alex Michelsen’s impressive run with a 6-0 7-6 (7-5) 6-3 victory over the 20-year-old American rising star.

Sinner looked in serious physical distress in the first few games of the pivotal third set on Monday before leaving the arena to receive treatment on the advice of his support staff when leading 3-2.

He returned to the court a rejuvenated man as the temperature in Melbourne reached 32 degrees - and presumably higher in the closed confines of Rod Laver Arena.

Three games later the 13th-seeded Rune called his own timeout for treatment on his right leg, only for Sinner to hold to love in the following game to claim the third set.

Another halt in proceedings came one game into the fourth set while officials repaired the bracket that holds the net in place.

Sinner stepped up the pace on the resumption and Rune was unable to respond as the Italian broke in the third game and again in the seventh before closing out the match in three hours and 13 minutes.

“I don’t want to talk so much about how I felt today. I was not feeling really well,” Sinner said in his post-match press conference.

“I was struggling physically, and I came here as late as possible as I knew that it was going to be very, very difficult, playing against a tough opponent but also playing against myself a little bit.

“I was a bit dizzy at times.”

Rather than the net delay being a distraction, Sinner said it was a blessing.

“At this point, 20 minutes off court, trying to get back physically, putting some cold water on my head, it was very helpful. It was big, big luck to me.”

The red-hot No.1 - who won his first two major titles last year at the Australian and US Opens - has only lost two matches since bowing out in the quarterfinals at Wimbledon and is now on an 18-match winning streak.

AAP