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 with either Australian No.1 Alex de Minaur or American Alex Michelsen.
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.
Jannik Sinner looked refreshed after taking a medical timeout in his win over Holger Rune. (James Ross/AAP PHOTOS)
He returned to Rod Laver Arena 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.
Officials worked hard to repair the net on Rod Laver Arena. (James Ross/AAP PHOTOS)
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 quarter-finals at Wimbledon and is now on an 18-match winning streak.
Rune pushed a weakened Sinner before succumbing in four sets. (James Ross/AAP PHOTOS)
The defending champion will face de Minaur in the quarter-finals after 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 was also joined in the last eight by Ben Shelton after the American's opponent, 38-year-old Gael Monfils, withdrew through exhaustion while trailing 7-6 (7-3) 6-7 (7-3) 6-6 (7-2) 1-0.
A semi-finalist at the US Open in 2023, Shelton reached the quarters at Melbourne Park in the same year which was his best result.
Shelton, 22, will face Lorenzo Sonego, who ensured there would be two Italian men's quarter-finalists at the Australian Open for only the second time.
Sonego ended the unlikely run of US qualifier Learner Tien, winning 6-3 6-2 3-6 6-1.
It was the first time the 29-year-old Sonego had advanced to the quarters at a major on his 22nd attempt.
