Roger Federer says if he felt his groin injury would have sidelined him for several weeks, he would have retired against Tennys Sandgren. Federer won the opening set 6-2 against the world No 100 but dropped the second set as his service speed dipped dramatically.
Then trailing 3-0 in the third set, Federer left the court for a medical timeout.
There was not an immediate improvement as Sandgren went two sets to one ahead but Federer saved seven match points in the fourth set to steal it in a tiebreak.
And then a much more looser Federer was the better player in the final set, winning it 6-3.
Federer is now into a record extending 46th Grand Slam semi-final and awaits the winner of Novak Djokovic and Milos Raonic.
Speaking after the match to Eurosport, Federer admitted he had to do some self-diagnosis and realised that the right groin injury he was dealing with was not as bad as feared.
He told Eurosport: “When you are having an issue, big or small, most important is that you know how bad it can get.
“If you feel like you can really injure yourself, it could cost weeks and months of the season, then it is obviously better to stop.
“But I felt like this a stiffness in my groin, hip and hamstring for a few days maximum and I have that.
“And then the question is how can you deal with it.
“So for me it was not bad enough to stop and I believe in miracles, you never know if he starts feeling bad, he’s also getting nervous and maybe carrying an injury I don’t know about.
“So [I said] lets just stay in the match, try some things out and if I can stay with him, you never know I might feel better.
“Because I know my problem and I know what I can and can’t do and things get very simple.
“You have no more expectations, it is all on the opponent and that’s when it gets quite difficult for him to play.
“It was a tough match for him and I’m sorry about it.
Looking ahead to his potential semi-final opponent, Federer said: “It’s great to see Milos doing well. It’s nice for him to remind everyone that he does belong up in the rankings. It will be a great match with Novak Djokovic.
“Novak is obviously a champ. He loves playing here. We have had some epic matches in the past. I hope I feel better than I do today otherwise I might as well be skiing in Switzerland.”