Roger Federer: Six-time Australian Open champion reflects on 'lucky' win against Tennys Sandgren

Roger Federer said he was "incredibly lucky" to save seven match points and pull off a second remarkable comeback of the Australian Open to reach the semi-finals.

The six-time champion in Melbourne admitted he was unaware just how many match points he had faced as the 38-year-old defeated world No 100 Tennys Sandgren 6-3 2-6 2-6 7-6 (10-8) 6-3.

Federer, who recovered from 4-8 in the final-set tie-break to beat John Millman in the third round, also struggled with a groin injury which forced him to take an off-court medical timeout at 0-3 in the third set.

Sandgren, who was aiming to reach the last four at a Grand Slam for the first time, held three match points at 4-5 in the fourth set and saw four further opportunities saved in the tie-break, before Federer completed a stunning win in the deciding set.

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Federer will continue his bid to win a record-extending 21st Grand Slam singles title against defending champion Novak Djokovic in the semi-finals.

"Honestly, when they told me seven, I was like, 'What?' I thought it was three. It's such a blur at some point," Federer said.

"I remember there were a few longer rallies on match points. I just said, 'If he can belt a backhand down the line, or run around and go huge, he's willing to take a chance', because you just don't know if you're going to get another opportunity for a match point like this.

"You've got to be a little bit careful. He did that. I thought it was the right play in that very moment by him. That's why I feel a bit bad in a way because I didn't feel like he did anything really wrong. It's just luck at some point.

"I've been on the other side as well. These ones just sting and they hurt. If you could obviously play them again, would you play them differently? But I could have blinked at the wrong time and shanked. That would have been it. I was incredibly lucky today."

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Federer was given a warning for swearing in the third game of the third set after being overheard by a line judge as his frustration about the tightness in his leg impacted on his performance.

"Only maybe when I won that fourth set did I really think that maybe this whole thing could turn around"

The Swiss, who has never retired from a professional match, conceded victory appeared to be beyond him against the stubborn resistance of Sandgren.

"For the most time there I thought that was it," he said.

"Of course, there's little sparkles where maybe not, then you're like, 'No, it is over'. Only maybe when I won that fourth set did I really think that maybe this whole thing could turn around."

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Federer and his semi-final opponent Djokovic share 13 out of the last 16 Australian Open titles and the former world No 1 is hopeful he can recover in time to produce near his best against the seven-time winner.

"You have an extra day, adrenaline, there's a lot of things. Two good nights of sleep, doctors, physios," Federer added.

"Hopefully we'll find out that it's actually nothing bad, that it was just the groin that went really tight from playing a lot, from nerves, I don't know.

"If I can get through a match like this, through a match like Millman, you do believe. I only believe it once it's over, I shake the hand of the opponent."

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