Sinner had his run of 29 consecutive sets won snapped by his 173rd-ranked opponent, but recovered to advance to the third round with a 4-6 6-4 6-1 6-3 victory on Rod Laver Arena on Thursday night.
Sinner is attempting to defend his title with a doping saga hanging over his head, with a Court of Arbitration for Sport hearing set to be heard in April.
Tristan Schoolkate showed plenty of determination in his second-round clash with Jannik Sinner. (Lukas Coch/AAP PHOTOS)
It comes after the World Anti-Doping Agency appealed against the sport's decision not to ban Sinner, despite the Italian testing positive twice for the anabolic steroid clostebol in March.
Sinner's problems were on-court early in Thursday night's encounter, as Schoolkate took it up to his much more accomplished opponent.
The West Australian broke to love in the decisive game of the first set and held his own serve until Sinner eventually converted his first break point of the match in the seventh game of the second set.
After that Sinner took over, the two-time major winner's class shining through as he dominated the third and fourth sets.
"It's always tough to play against a player I don't know very well," Sinner said.
"He was serving really well and he was playing much better in the beginning than I was, obviously.
"I know with the crowd it was an amazing atmosphere ... it's a very special place, especially for the Australians to play here with the home crowd.
"But I have to be very happy still for my performance and never taking things for granted, so I'm very glad to be again in the next round."
Sinner now boasts a 15-0 record against players at their home grand slams, including three against Australians at Melbourne Park after wins over Max Purcell (2020) and Alex de Minaur (2022).
His latest victory set up a third-round meeting with American world No.46 Marcos Giron, who outlasted Argentina's Tomas Martin Etcheverry 7-5 3-6 7-5 3-6 6-4.
Schoolkate had reached the second round by beating Japan's Taro Daniel and relished his first experience on Rod Laver Arena against the world's best.
The 23-year-old took huge positives out of his second grand slam appearance, after also reaching the second round on debut at last year's US Open.
🔥 meets 🧊— #AusOpen (@AustralianOpen) @JohnMcEnroe asking for tips to control his emotions?! You cannot be serious! 🤣#AO2025 • @janniksin pic.twitter.com/vELR0lS7OXJanuary 16, 2025
"I was super happy with the way I backed myself in for the first set especially," Schoolkate said.
"I played great tennis, I thought I served very well, kept myself in the set and when I had the chance to break serve, I did and came away with the set ... it was pretty cool."
Schoolkate, who relished the huge home crowd cheering him on, felt his performance was testament to the work he's been doing out of the limelight.
"I feel like I'm improving year after year and feel like I've come a long way," he said.
"To test myself against the best in the world and have some success in the match was really good.
"It gives me a lot of belief that what I'm doing is working and if I can keep working on my game and keep improving, well, hopefully I can take another set of maybe even a match off players like this."
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