MELBOURNE, Jan. 24 (Xinhua) -- World No. 2 Jannik Sinner overcame cramps and survived a major third-round challenge from Eliot Spizzirri of the United States to keep his Australian Open title defense alive on Saturday.

The Italian's bid for a third straight triumph in Melbourne remains on track after he beat the American 4-6, 6-3, 6-4, 6-4 in three hours and 45 minutes.

As temperatures soared at Rod Laver Arena, the four-time Grand Slam champion needed medical attention early in the third set after struggling with cramps.

On resumption, he labored around the court as Spizzirri capitalized to lead 3-1 before play was suspended due to the closure of the retractable roof as the extreme heat reached an unbearable level.

The match turned as a relieved Sinner took control against the 85th-ranked Spizzirri.

"He played really, really well. I struggled physically today and I got lucky with the heat rule. Very happy with my performance," Sinner said.

With the match in the balance, Sinner appeared set to essentially relinquish the third set before play was halted.

The Italian came back rejuvenated although still limited in his movement as his strategy to shorten the points proved a masterstroke.

Sinner sealed the third set with an ace and finally broke Spizzirri's spirit in the fourth set.

He will play compatriot Luciano Darderi in the last 16.