Australian Open 2020 news - Roger Federer: I lost count of how many match points I had to save

After winning the first set against the American, Federer lost the second and needed to undergo a medical time out during the third, during which he was also eventually bettered.

In the fourth, he had to save three match points on his own serve before facing four more in the tiebreaker, which he eventually won 10-8, before winning the decider 6-3.

"It is [a miracle] for sure - super lucky today. Apparently I saved seven match points, I wasn't sure how many, a lot, too many," he told Eurosport after his second five-set win of the tournament.

"This normally doesn't go your way. I've had some lucky ones in the past, I've also had some heartbreak losses obviously so it's nice that they even out throughout your career.

"This one is tough for Sandgren because he did everything right, he was the better player."

Federer also revealed that he did not elect to retire from the match when he was injured as he knew that he could soldier on without causing himself serious damage, while hoping that his opponent would get tight.

"I really started to struggle with my leg throughout the match. I just tried to stay out there and make a match of it and make him win it, not just me giving it to him. I was able to do that until the very end, it's unbelievable. I don't know how I escaped but it was a lucky one.

"When you're having an issue, however big or small, most important is that you know how bad it can get. If you feel like you could really injure yourself and it could cost you weeks or months of the season then it's obviously better to stop but I felt like it was a stiffness in my groin, in my hip, in my hamstring for a few days maximum. Then the question is: how can you deal with it?

"You never know if he starts feeling bad, it's not like he's not played this tournament as well. He's maybe getting nervous, maybe he's carrying an injury I don't know about, so let's just stay in the match, let's try some things out, you never know. I could have felt better because I know my problem and I know what I can and can't do.

"And then things get very simple, you have no expectations and it's all on the opponent and that's when it gets difficult for him to play. It was a tough match for him and I know that."

Federer will play the winner of the quarter-final between Novak Djokovic and Milos Raonic in the next round as he looks to reach his eighth Australian Open final.

Speaking in the Eurosport studio, Mats Wilander said that Federer’s comeback was the biggest miracle he had ever seen in tennis.

“I don’t think anyone except maybe Tennys Sandgren, I think he’s the only one who knew this is not in the bag,” he said. “It’s tough to play a tennis match when your opponent is clearly injured. Especially when your opponent is the favourite and you have one chance in a lifetime to reach the semis of a Grand Slam.

“So I feel so bad for Tennys Sandgren but Roger Federer pulls this match out because first of all he refuses to retire and second of all he has so many different options in his game. And even limping around, not running full he can still find a way to hit different spins, serve well, come to the net, make his opponent wonder, get worse…

“I mean literally, like Roger said, he does believe in miracles and that to me… I don’t know if I’ve ever seen a bigger miracle on a tennis court.”