Gutsy three-time Australian Open finalist Daniil Medvedev fought back from two sets down to reach the last 16 on Friday against unseeded Fabian Marozsan of Hungary.
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The Russian 11th seed battled through 6-7 (5/7), 4-6, 7-5, 6-0, 6-3 in 3hr 43min.
He will meet 25th seed Learner Tien of the United States after he beat Nuno Borges of Portugal in straight sets.
It was the fifth time in his career that the former world No 1 Medvedev had come back from 2-0 down to win a match.
"It was a very tough match," said the 2021 US Open champion, who had a wretched major record last year.
"I managed to stay strong and I am happy about it.
"He played really well and I was like, if I lose, I lose, but I am going to fight."
The sometimes combustible Medvedev was pleased that he kept his volatile temper under control.
"I did manage to stay calm, even in the fifth set and managed to hit some good shots even in the fifth," he said.
Marozsan, ranked 47, was bidding to reach the last 16 of a Grand Slam for the first time.
They exchanged breaks to start in a sign of things to come.
The two players went to a first-set tiebreak, where the Hungarian edged in front and held his nerve on his second set point.
The feisty 29-year-old Medvedev had vowed to be more "positive" on court after a 2025 where he lost in the first round at the French Open, Wimbledon and US Open and was bundled out in round two in Melbourne.
His emotions began showing and he was on the ropes as he fell 4-1 down in the second set in the Margaret Court Arena sunshine.
Medvedev, who warmed up for Melbourne by winning the Brisbane title, reined in his emotions and got one break back, but Marozsan sealed the second set.
The unseeded 26-year-old appeared in control and homing in on victory, but back roared Medvedev to turn the tide dramatically.
With his serve showing signs of firing he won the third set and took that momentum into the fourth, the Russian racing through the set without dropping a game in just 19 minutes.
It sent a gripping match into a deciding set, where both struggled to hold serve, before Medvedev scraped through.
"Five sets again," he wrote afterwards on the on-court camera.
Medvedev has reached three of the last five finals in Melbourne.
He was outplayed by Novak Djokovic in 2021 before a heart-wrenching defeat to Rafael Nadal a year later.
He imploded against Jannik Sinner in 2024, crashing in five sets after being two up.