Federer saves seven match points in 'miracle' escape

The six-time champion, struggling physically, saved three match points at 4-5 in the fourth set and four more in the tie-breaker to win 6-3, 2-6, 2-6, 7-6 (10/8), 6-3 and set up a clash against either title-holder Novak Djokovic or Milos Raonic.

Federer received a rare warning for an audible obscenity before going off-court for treatment on a groin injury in the third set, but still looked hampered as he forced a fifth set against the big-serving American.

"I believe in miracles," Federer said, revealing that he thought his groin strain had ended his chances. "There could be rain, there could be all kinds of stuff.

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"(I thought) just let him finish me off in style, and he didn't do that. I'm incredibly lucky tonight, today -- I don't even know what time it is."

Sandgren, achingly close to becoming the lowest-ranked player to beat Federer at the Australian Open, can count himself unlucky especially after a ball girl accidentally collided with him during the pivotal tie-breaker, which he lost.

Federer has made heavy weather of reaching his 46th Major semi-final. He was two points from defeat by John Millman in a fifth-set tie-breaker in round three, and dropped a set against 67th-ranked Marton Fucsovics in round four.

- 'Quiet little life' -

In the women's draw Australia's world number one Ashleigh Barty dismissed two-time Wimbledon champion Petra Kvitova in impressive style to reach the semis for the first time.

The unflappable Barty beat the Czech 7-6 (8/6), 6-2 and will be favourite in her semi-final against America's Sofia Kenin -- sending hopes soaring of a first home winner in 42 years.

The French Open champion, who once quit tennis to play cricket and has been steadily rising since her return, is the tournament's poster girl with her image plastered all over Melbourne.

But she said: "I'd prefer to just be sitting at home just living my quiet little life."

Kenin, whose career is also on the up, made her first Grand Slam semi-final and with it will rise to at least 12 in the rankings -- making her the second-highest American behind Serena Williams.

The feisty 21-year-old was a 6-4, 6-4 winner over Ons Jabeur, halting the Tunisian's historic run which made her the first Arab woman to reach a Major quarter-final.

"She's a really tough player, I knew she's going to come out playing strong," Kenin said. "She's had really good matches, good wins. It wasn't an easy battle -- all respect to her."

Jabeur has ignited interest back home with her run to the last eight, even receiving a good-luck phone call from her president.

"I think I proved that I can be in the quarter-finals in a Grand Slam, even if I have a lot of things to improve physically and mentally," said the 25-year-old, who will now move inside the top 50.

"I proved to myself that I could do a lot of great things. I'm happy that I played this way."