A hobbling Sinner looked in huge bother when trailing by a service break midway through the pivotal third set before divine intervention from the weather gods helped the world No.2 to a dramatic victory over unfancied American Eliot Spizzirri on Saturday.
Immediately after falling behind 3-1 in the third stanza, the Open's extreme heat policy was applied, offering the Italian superstar a mighty reprieve as the roof was closed on Rod Laver Arena.
Sinner returned to the court following the brief resumption to swiftly break straight back before going on to eke out a gruelling 4-6 6-3 6-4 6-4 third-round triumph.
Spizzirri was philosophical in defeat, shrugging they are "the rules of the game and you gotta live with it", while Sinner drew a big sigh of relief.
"I struggled physically a bit today. We saw this. I got lucky with the heat rule, when they closed the roof," the four-time grand slam champion said.
"I took my took my time and, as the time passed, I felt better and better and I'm very happy about this performance."
As the mercury soared past 36 degrees at Melbourne Park, and even more on court, Sinner looked frazzled and red-faced even before his physical conditioning began to fail him.
He inexplicably dropped three successive service games to concede the opening set and trail by a break in the second.
Compounding his troubles, the second seed received a time violation from chair umpire Fergus Murphy as tensions simmered and Spizzirri threatened a massive grand slam boilover.
Sinner, though, stayed cool to turn the set around and level the match up.
But still more troubles lay ahead, with Sinner needing some pickle juice and treatment for calf cramping before the fourth game of the third set.
"Go point by point, mate. Dig deep," Australian super-coach Darren Cahill urged his charge from the champ's courtside pod.
"You've just got to get through the third set, mate. Even if you walk around. Don't worry."
But the four-time slam winner and two-time defending Open champion could barely even move after losing a sapping 20-shot rally, then receiving a second time violation and dropping serve to go 3-1 behind.
In an extraordinary piece of timing, the extreme heat policy was applied as soon as Sinner dropped serve.
TV footage captured Cahill following tournament director Craig Tiley down the Melbourne Park hallways as the RLA roof was being closed.
But while Spizzirri cursed his bad luck, Sinner was thrilled to have avoided his worst-ever loss, rankings wise, at Melbourne Park.
His reward for taking out the world No.85 is an all-Italian last-16 showdown with 22nd seed Luciano Darderi on Monday.
"Looking back, in every big tournament I've had, there were some really tough matches, so hopefully this can give me some positives for the next round," Sinner said.
Darderi also showed his mettle to oust Russian world No.18 Karen Khachanov 7-6 (7-5) 3-6 6-3 6-4 on Kia Arena.
And rounding out an historic, if testing, day for Italian tennis, fifth seed Lorenzo Musetti gave the Davis Cup champions three men in the fourth round for the first time with a 6-7 6-4 6-2 5-7 6-2 win Czech Tomas Machac.
"Happy that this finished," Musetti said after inflicting the first defeat of the year on Machac.
"We fought really hard. I knew it before starting the match that today with the heat I was prepared to fight 'til the end."
Musetti will face ninth seed Taylor Fritz, who ended 40-year-old 2014 champion Stan Wawrinka's Australian Open swan song 7-6 (7-5) 2-6 6-4 6-4.
World No.8 Ben Shelton advanced with a minimum of fuss, beating Swiss 30th seed Valentin Vacherot 6-4 6-4 7-6 (7-5) to book a fourth-round date with either 2018 runner-up Marin Cilic or 12th seed Casper Ruud.
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