Roger Federer saves match points and overcomes injury to beat Tennys Sandgren

Roger Federer staged his second Houdini act of the Australian Open to defeat Tennys Sandgren and reach the semi-finals.

This comeback was even more dramatic than his third-round victory over John Millman, where Federer recovered from 8-4 in the deciding tie-break.

Here, he was clearly physically below his best, taking an off-court medical timeout in the third set, but saved seven match points in the fourth on his way to a 6-3 2-6 2-6 7-6 (8) 6-3 victory.

Federer was struggling to move to his forehand side and looking nothing like the player who has won 20 grand slam titles.

American Sandgren, ranked 100 and playing in the biggest match of his life, had three chances at 5-4 in the fourth set but made unforced errors on all of them.

He then led 6-3 in the tie-break and had a further chance but Federer, who has never retired from a professional match, simply refused to be beaten.

He loosened up a little and forced a set point on his own serve, wagging his finger as Sandgren sent the ball flying long.

And Federer ensured those heroic efforts were not in vain, freeing himself up to win the fifth set after three hours and 31 minutes.

The 38-year-old seemed to have had his major scare against Millman, although he was still far from his best against Marton Fucsovics in round four, fighting back from a set down.

Both those matches were played at night, and the sunshine seemed to help Federer as he eased to the first set against Sandgren, who was looking to become the lowest-ranked man to reach the semi-finals here for nearly 30 years.

But Federer’s problems began when he dropped serve in the second game of the second set, his usually-reliable forehand breaking down with alarming regularity.

He was furious to receive a warning in the third game of the third set after a line judge reported him swearing, but that was a trivial matter compared to what was going on with his body.

The Swiss revealed afterwards he was struggling with a tight groin, and it seemed highly unlikely he would be able to fight through it.

But fight he did, and he could now face great rival Novak Djokovic in the last four on Thursday.