Roger Federer's winning run at the Australian Open ended with "massive regrets" after his loss to 20-year-old Stefanos Tsitsipas.

The Greek, who was not born when Federer made his professional debut, has rapidly established himself as one of the most exciting up-and-coming talents in the game and backed it up spectacularly with a 6-7 (11), 7-6 (3), 7-5, 7-6 (5) victory to move through to a first grand slam quarter-final.

Federer had not lost a match at Melbourne Park since a semi-final defeat to Novak Djokovic in 2016 but his often brilliant forehand was wayward, especially at the big moments, and he failed to take four set points in the second set that might well have changed the outcome.

The 37-year-old saw 12 break points come and go in the match, and he made no attempt to hide what a hurtful defeat it was, saying: "I have massive regrets tonight.

"I felt like I have to win the second set. I don't care how I do it, but I have to do it. [It] cost me the game tonight.

"I lost to a better player who was playing very well. He 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."

Tsitsipas grew up idolising Federer and there was certainly something of the young Swiss in his opponent, from the flowing single-handed backhand, the willingness to charge the net, and the confidence to believe he could beat his childhood idol, just as Federer did to Pete Sampras at Wimbledon in 2001.

"He has a one-handed backhand and I used to have long hair, too," said Federer pithily. "So maybe a little bit [similar], sure."

John McEnroe declared the result to be a changing of the guard, but Federer is clearly not about to hand over the mantle just yet and announced he had decided to play on clay this year after missing the French Open for the last three years.

"He's in front of the mic a lot," Federer said of McEnroe. "He's always going to say stuff. I love John. I've heard that story the last 10 years. From that standpoint, nothing new there.

"Stefanos has definitely done a really nice job now the last year-and-a-half. Before that, too, obviously. But beating Novak [Djokovic] in Toronto, the likes of [Kevin] Anderson and [Alexander] Zverev, now me here. That's what you need to do to get to the next level.

"I see him definitely being high up in the game for a long time. That was a good night for him tonight."

Asked for his feelings when he won the final point, Tsitsipas said he had flashbacks of watching Federer as a child.

"Just happiness, pure happiness," he said. "It was a very emotional moment. It was a beginning of something really big. I felt joy. I felt a huge relief going out of my shoulders.

"That moment is definitely something that I will never, ever, ever forget. I just managed to close that match and stay strong, beat my idol. My idol today became pretty much my rival."

Asked if he believes he can go all the way and win the title, Tsitsipas said: "For sure. That's why I'm here. That's why I'm playing, for the trophy. I feel good. I really want it badly."

While Federer must head home licking his wounds, Rafael Nadal's prospects of winning a second Australian Open title 10 years after his first are looking ever more rosy.

The Spaniard was ruthless in the first two sets against Tomas Berdych and then saved a set point in the third in a 6-0, 6-1, 7-6 (5) victory.

Nadal finds himself as the only man in his half of the draw who has previously experienced a slam quarter-final.

He will take on another of the next generation in American Frances Tiafoe, who celebrated his 21st birthday by emotionally defeating Grigor Dimitrov 7-5, 7-6 (6), 6-7 (1), 7-5.

Tsitsipas, meanwhile, next faces Spaniard Roberto Bautista Agut, who claimed his latest scalp with a 6-7 (6), 6-3, 6-2, 4-6, 6-4 victory over last year's runner-up, Marin Cilic, to win a fourth-round match at a slam for the first time in 10 attempts.

It was Bautista Agut's third five-set match after wins over Andy Murray and John Millman, while he has also taken out 10th seed Karen Khachanov.