Roger Federer admitted he was unsure if he'd won a key point after a double-bounce in his stirring Australian Open quarter-final victory over Andy Murray.

An agitated Murray questioned whether Federer had reached the ball before it bounced twice before breaking the Scot to claim a 5-4 advantage in the third set and an opportunity to serve out the match on Wednesday night.

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Did Federer really bounce back?

Roger Federer admits he's unsure if a key point made in last night's quarter final against Andy Murray was legal. See for yourself.

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Television replays proved inconclusive, with former world No.1s Jim Courier and Lleyton Hewitt initially both unsure.

But after taking several more looks, Courier said it was "60-40 that it hit the ground first" - and 70 per cent of TV viewers on a Channel Seven poll agreed when the fans were initially asked to vote.

"But it's impossible for [umpire] Pascal Maria to know and for Roger to know," Courier said.

Talking point: did the ball bounce twice?

Talking point: did the ball bounce twice? Photo: Channel Seven

Federer, who was unable to serve the match out the very next game after the incident before going on to win 6-3, 6-4, 6-7 (6-8), 6-3, said he "honestly" didn't know if it was a double-hop or not.

"I thought I probably got it, especially the way it bounced on the other side," he said after booking a semi-final showdown on Friday night with world No.1 Rafael Nadal.

"It felt like I got under it. At that point, I might even have my eyes closed. It's like it's so extreme that I really don't know.

Roger Federer was unsure if there was a double bounce.

Roger Federer was unsure if there was a double bounce. Photo: Joe Armao

"We'll have to check the replay time and time again."

But the Swiss superstar, a nine-times winner of the ATP's Stefan Edberg Sportsmanship Award, said he was disappointed the shot was immediately replayed twice on the big screen at Rod Laver Arena.

"I just told the umpire: 'How can they show this and create this controversial moment potentially?' It's not really what you want to do," Federer said.

Upset: Andy Murray thought the ball bounced twice.

Upset: Andy Murray thought the ball bounced twice. Photo: AFP

"I hope it was played the right way. If it wasn't, I'm sorry.

"But it's an umpire's call. I've been burnt by these calls before.

"I can't remember the score, but clearly it was a big one. I think I ended up breaking him in the game."

Roger Federer plays a shot. Click for more photos

Australian Open: Andy Murray v Roger Federer

Roger Federer plays a shot. Photo: AFP

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