'I got incredibly lucky': Comeback king Roger Federer saves SEVEN match points to reach Australian Open semi-finals (VIDEO)

It was anything but easy, but Roger Federer showed he still has plenty of fighting spirit as he battled back from the brink to defeat Tennys Sandgren and reach the semi-finals of the Australian Open in Melbourne.

Roger Federer staged a dramatic rearguard action as he saved SEVEN match points before eventually defeating America's world number 100 Tennys Sandgren in Tuesday's quarter-final clash.

Federer took the win 6-3, 2-6, 2-6, 7-6, 6-3 in a rollercoaster of a match that saw Sandgren produce some outstanding tennis to come back from a set down to find himself on the brink of a memorable victory. But, for the second time this week, Federer produced a sprited fightback to eventually defeat his man and move into the final four of the men's draw.

Earlier in the week Federer had already endured a marathon five-setter against Australian John Millman and won six points in a row from 8-4 down in the final-set tiebreaker to scrape through.

And the Swiss superstar was in even worse trouble against Sandgren, before somehow finding the form to save a plethora of match points before converting his own to reach the semis.

"You've got to get lucky sometimes," said a smiling Federer after the match.

"I tell you that because, in those seven match points, you're not in control.

"I was just hoping that maybe he wasn't going to smash a winner, if he misses one or two, who knows what's going to happen? I think I got incredibly lucky today.

"I don't deserve this one but I'm still standing here and I'm obviously very, very happy."

The strain on Federer was clear to see during the match, as he was handed a warning for an uncharacteristic verbal obscenity, then engaged in an argument with umpire Marijana Veljovic before leaving the court for a medical time out for a supposed groin injury.

The interruption didn't appear to affect Sandgren, who went on to win the set, but the American was unable to convert his 2-1 set lead into a victory as Federer staged his dramatic comeback.

"(The) draws are not getting easier. With these lucky escapes, you might play without expectations because you know you should be skiing in Switzerland," said Federer.

"(I'm) lucky to be here, (so I) may as well make the most of it. I better feel better than today (in the semis), otherwise I am really going skiing."