Sinner sails through after rare stumble at Australian Open while Medvedev loses marathon match

World No 1 Jannik Sinner dropped a set for the first time in 14 matches before going on to beat wildcard Tristan Schoolkate in four sets at the Australian Open on Thursday.

The defending champion fought back after a slow start to seal his third-round spot with a 4-6, 6-4, 6-1, 6-3 victory against the world No 173.

It was the first time Sinner, who claimed his first Grand Slam title when he defeated Daniil Medvedev at Melbourne Park last year, had conceded a set since October's Shanghai Masters.

Western Australian Schoolkate ended the streak inside 47 minutes by converting the only break point of the opening set to the delight of a partisan crowd inside a cool and breezy Rod Laver Arena.

Sinner continued to struggle to get a handle on Schoolkate's game early in the second set but a rasping crosscourt winner earned him a break for 4-3 and from then on the match was only going one way.

"It's always tough to play against someone I don't know very well. He was playing much better than I was at the beginning," said the Italian, 23, who is the youngest player to win nine successive men's singles matches at the Australian Open since Novak Djokovic between 2008 and 2009.

"I have to be very happy with my performance and never take things for granted. Very glad to be in the next round. I can improve, yes, but I'll take it."

Next up for Sinner as he looks to build on his hardcourt Grand Slam titles in Melbourne and New York last year is American world No 46 Marcos Giron.

Last year's runner-up Daniil Medvedev was dumped out in the second round early on Friday morning by 19-year-old qualifier Learner Tien in a massive Melbourne shock.

The American ranked 121 stunned the world No 5 6-3, 7-6, 6-7, 1-6, 7-6 in a nail-biter and faces France's Corentin Moutet in the next round in his debut Australian Open.

With the time ticking towards 3:00 am, the left-handed Californian Tien soaked up the applause at Margaret Court Arena after a match that lasted four hours and 48 minutes.

Teenage rising star Joao Fonseca said nerves got the better of him after being bundled out by Italian Lorenzo Sonego in a five-set thriller.

The highly rated Brazilian, 18, burst on the scene by stunning ninth seed Andrey Rublev in round one and looked on track for another upset when he won the first set.

But in a seesawing battle, the 55th-ranked Sonego clawed through 6-7, 6-3, 6-1, 3-6, 6-3 after three hours and 37 minutes of high-quality tennis.

The loss ended a 14-match win streak for Fonseca, who was making his Grand Slam debut in Melbourne and was tipped for the top by Carlos Alcaraz and Novak Djokovic this week.

"My first time playing five sets. I knew it was going to be a tough battle," he said.

"I didn't play my best today. I was a little bit nervous. Actually a lot nervous in the second and third set.

"But it was a great two months," he added. "I mean, doing 15 matches consecutively and then winning 14, it's amazing. Good start to the year.

"Now work more and more to be more prepared for those matches."

Sonego's reward in a clash against Hungary's Fabian Marozsan, who took down 17th seed Frances Tiafoe, also in five sets.

Home hope and eighth seed Alex de Minaur claimed a 6-2, 6-4, 6-3 win over American qualifier Tristan Boyer, while fourth seed Taylor Fritz needed just 82 minutes to beat Chilean qualifier Cristian Garin 6-2, 6-1, 6-0.

American Fritz also revealed he is donating his first-round prize money ($81,700) to help people affected by the California wildfires.

"I just want everyone to stay safe, it's just insane what happened," said Fritz, who used to live in Los Angeles and has family and friends affected.

"I wanted to say something after my first-round match but I'm going to be donating my first-round prize money to LA wildfire relief funds.

"It's really the least I could do. Southern California's my home and LA was my home for a very long time so I'm just doing what I can do to help. "