Here's what went wrong for Federer at Australian Open

'It definitely didn't go the way I was hoping on the breakpoints'

If having his Australian Open title defence ended early was not painful enough for Roger Federer, on Sunday, there was the additional sting of being beaten by a tyro with plenty of similarities to his younger, fearless self.

Sporting a one-handed backhand and a mop of long hair, Stefanos Tsitsipas cared little for reputation or records as he toppled the 37-year-old Swiss master 6-7(11), 7-6(3), 7-5, 7-6(5) at a packed Rod Laver Arena.

There was no being overawed by the occasion or freezing in the clutch points, nor any of the failings that have tripped up so many of the young pretenders who have shared a court with the 20-times Grand Slam champion.

There was only composure and brilliance from the 20-year-old Tsitsipas who became Greece's first Grand Slam quarter-finalist and seems destined for bigger prizes in the near future.

In short, he was not unlike the Federer of the early 2000s who crashed through the game's titans with fearless abandon and condemned a 35-year-old Andre Agassi to defeat in the 2005 U.S. Open final.

After exiting Melbourne Park without a quarter-final for only the second time in the last 18 years, the Swiss shrugged off a suggestion from John McEnroe that the Rod Laver Arena crowd had just witnessed a "changing of the guard".

"Yeah, sure. He's in front of the mic (microphone) a lot," a downcast Federer told reporters.

"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."

Federer will note ruefully, however, that he has now been upset in the fourth round at two Grand Slams in succession, having been tipped out of the U.S. Open by unseeded Australian John Millman.

His legs seemed heavy and his groundstrokes lacked punch towards the end of the Tsitsipas clash, which saw both players scramble hard for three hours and 45 minutes.

For Federer, the most galling part was his lack of a clinical edge.

He left all 12 break points he grabbed from the Greek go unconverted and blew four set points that would have given him a two-set lead.

"It definitely didn't go the way I was hoping on the breakpoints," he said. "Nevertheless, it's very frustrating."

"I lost to a better player who was playing very well tonight. Hung in there, gave himself chances at some point, stayed calm."

"It's not always easy, especially for younger guys."