With the match level still at one set, Sinner could barely walk at the start of the third set and lost serve 3-1.

Seconds into the fourth game, with Sinner looking set to expire, the Australian Open’s heat stress meter reached five — meaning the top seed was able to walk off the court for treatment.

There’s no doubt the Heat rule benefited Sinner, who immediately limped into the locker room.

Sinner broke immediately after an eight-minute delay while the roof of Rod Laver Arena was closed according to the referee.

While still tentatively moving, a calmer Sinner managed to win another Spizzeri serve to take a 5-4 lead and secure the third set before going on to claim a thrilling victory.

Play at the Australian Open stops when the heat stress meter reaches the maximum of five.

Matches at the exhibition courts – which include Laver – stop at the end of a tight match so the roof can be closed and the air circulation system allowed to cool the stadium.

The temperature dropped to around 26 degrees Celsius during the fourth set of Sinner’s match.

Sinner now looked more comfortable in his movement, although he often remained standing at shifting flanks, and striking the ball became too much for Spizzeri.