The Italian top seed had no answers at the start against Australian wildcard Tristan Schoolkate, ranked 173, but found his groove to win 4-6, 6-4, 6-1, 6-3 on centre court.

It was his 16th consecutive victory in an ominous sign for next opponent Marcos Giron in round three.

The American punched his ticket by beating Argentina's Tomas Martin Etcheverry, who was the last person before Schoolkate to take a set off Sinner.

That was back in late September at the Shanghai Masters. Since then, Sinner had won 29 consecutive sets.

"It's always tough to play against a player I don't know very well. I felt like he was serving really well, playing much better in the beginning than I was," said Sinner.

"But I am still very happy with my performance. You can never take things for granted so very glad to be in the next round.

"It was a very tough match. I can improve, yes," he added.

The 23-year-old, who is defending a Grand Slam title for the first time after his five-set win against Daniil Medvedev in last year's final, was out-of-sorts initially.

Schoolkate belied his ranking, going toe-to-toe in the first set and stunning Sinner by breaking to love at 5-4 when the Italian slammed a forehand into the net.

Sinner's serve was not firing and he uncharacteristically committed eight unforced errors while hitting just six winners.

But he slowly started to get the measure of the Australian, who is on his Grand Slam debut, and broke to love with a forehand winner to take a decisive 4-3 lead in set two.

Schoolkate's resolve faded and a net winner from Sinner gave him an immediate break in the third set as he won four games in a row to take the match out of reach.

The fourth set was a formality with Sinner in the zone.

Sinner is favourite to lift the trophy again at Melbourne Park after a sensational 2024 saw him become the top-ranked player in men's tennis.

Along with the Australian Open title, he added the US Open and ATP Finals crowns, winning eight tournaments altogether.