In a scintillating contest on Rod Laver Arena on Sunday night, 37-year-old Federer could not overcome his 20-year-old opponent who claimed a 6-7 (11-13) 7-6 (7-3) 7-5 7-6 (7-5) victory to continue his magical run at Melbourne Park.

The 14th-seeded Tsitsipas will face Spain's Roberto Bautista Agut in the quarter-finals and could meet Rafael Nadal in the final four.

Federer appeared to be in tears as he waved to fans upon exiting the hallowed centre court - the scene of so many triumphs - for what may be the final time.

Having never previously progressed beyond the fourth round at a major, an emotional Tsitsipas was lost for words after prevailing in a fourth-set tiebreaker.

"There's nothing I can describe it to," he said.

"I'm the happiest man on earth right now.

"Roger is a legend of the sport ... I've been analysing him since the age of six. It was a dream come true for me just being on Rod Laver Arena facing him."

Both men traded stunning winners throughout but Federer was made to pay the price for an unusually high 55 unforced errors.

Rising to the occasion in spectacular fashion, Tsitsipas saved 12 break points to hold serve for the match and deny Federer an opening.

"I also didn't break him at the Hopman Cup, so clearly something is wrong how I return him, what I'm trying to do," Federer said.

"He's doing a good job to defend them. Nevertheless, it's very frustrating."

The tone was set for a high-quality encounter in a tense first game which lasted eight minutes and included Tsitsipas being penalised for exceeding the 25-second shot clock when serving.

Federer, in a sign of early tension, then accused the chair umpire of having a "bad conscience" about the Tsitsipas violation when he awarded the young gun a point on challenge that Federer felt should have been replayed.

After prevailing in a tiebreak to take the first set in just shy of an hour, Federer had opportunities to press his advantage but couldn't finish his work.

The 20-time grand-slam title winner had four set points on Tsitsipas's serve up 5-4 in the second but failed to convert any as his junior opponent showed nerves of steel - something Federer conceded was a turning point in the match.

"I have massive regrets tonight ... I felt like I have to win the second set," he said.

"I don't care how I do it but I have to do it. Cost me the game tonight."

Leading two sets to one, Tsitsipas called for a trainer during the fourth set to massage his sore quads but continued to match Federer at every opportunity.

A dejected Federer said he had been unable to match Tsitsipas when it mattered.

"I lost to a better player who was playing very well tonight," he said.

"Hung in there, gave himself chances at some point, stayed calm. It's not always easy, especially for younger guys. Credit to him for taking care of that."

Australian Associated Press