Six-time champion Roger Federer said it was a "big relief" to survive an epic five-set marathon and seal his 100th Australian Open win on Friday, fending off a dogged challenge from John Millman.
The Swiss master was rattled by the all-guns-blazing Australian, but scraped through 4-6, 7-6 (7/2), 6-4, 4-6, 7-6 (10/8) to stay alive in his quest for a 21st Grand Slam title.
He will take on unseeded Hungarian Marton Fucsovics, who eased past American Tommy Paul in straight sets, for a place in the last eight.
"It was tough tonight, thank God it was a super breaker," said the third seed, who looked out for the count when he was down 8-4 in the best-of-10 fifth set super tiebreaker.
"He played a great match. It came down to the wire. What a match.
"This one was unique in many ways that I was able to turn a super breaker around like this in an atmosphere, it was crazy, fun, and I couldn't be more happy. Big relief."
"Things were extremely difficult, not just in the breaker, (but) throughout the match for me against John," he added.
Millman said he "left it all out there" and praised Federer, saying: "That's what the best players I guess do."
Federer not only gained a 100th victory at Melbourne Park but became the only player, man or woman, to post a century of victories at two different Slams.
The Swiss great reached three figures at Wimbledon last year.
He is one of only four players in the 100 club -- Martina Navratilova at Wimbledon, and Chris Evert and Serena Williams at the US Open, are the others.
It nearly didn't happen against the 47th-ranked Australian Millman, who memorably beat Federer over four gruelling sets in the round of 16 at the US Open in 2018.
One of the fittest players on tour, Millman broke Federer in the fourth game of the opening set.
The 38-year-old Federer, struggling to find his rhythm, fell 5-2 behind. He broke in the ninth game only for Millman to immediately break back to love thanks to poor Federer serving and take the set.
The second went with serve until the Swiss took his game to another level in the tiebreaker.
Federer wrestled control as he won the third set, but Millman came roaring back, excelling in the baselines rallies to break for a 4-3 lead and take the match into a fifth set.
The pair shared breaks in the tense decider and it went to a tiebreak with Federer looking dead and buried at 8-4 down.
But he stayed calm and hauled himself back to win a Grand Slam classic.
Third seed Roger Federer survived a huge scare to stay alive at the Australian Open