Sharapova hasn't beaten Williams since 2004, and one - perhaps slightly disrespectful - journalist asked Williams previous year if such a one-sided rivalry was really a rivalry at all.

Federer, a 17-time Grand Slam champion who has won the tournament four times, beat Tomas Berdych 7-6 (7-4) 6-2 6-4, while top seed and defending champion Djokovic saw off Japan's Kei Nishikori 6-3 6-2 6-4.

Federer is also 34 and it has been quite some time since he was able to take for granted advancement to the last four at Grand Slams.

A few years ago, the Australian Open and the other majors could have been called "Roger's World" - when Roger Federer was No. 1, still dominating men's tennis and the favourite face of sponsors.

The defeat came after Williams had enjoyed a phenomenal 2013 season, in which she reclaimed the world number one ranking, won the French and US Opens among eleven titles, and banked over $12 million in prize money.

Meanwhile, Radwanska booked her spot in the Australian Open semifinals for the second time, winning over Carla Suárez Navarro 6-1, 6-3 in the first match of the day on Rod Laver Arena.

Other than that final, which went to three sets, Radwanska has failed to win a set against Williams in seven other meetings.

Sharapova served 21 aces in her last match. But back-to-back double faults gave Serena the break point to tie the game at 2-2.

On the women's side, two-time former champion Victoria Azarenka is bidding to continue her strong form - she hasn't dropped a set in four matches and has lost only 11 games - when she plays Angelique Kerber. Sharapova remain resilient, saving three set points with a two big second serves and a forehand into the net from Serena, before finally losing the fourth break point.

Sharapova's first-serve percentage was falling and she went 0-40 down in the seventh game before showing grit to fend off the break points and claw back. "Certainly I was trying to just concentrate on the match when I was out there, but, like I said, it's been a hard, hard few days".

Next for Murray will be No. 8 David Ferrer, a two-time semifinalist, who held off No. 10-seeded John Isner 6-4, 6-4, 7-5.

"I'm very, very happy", said Federer.

"It's obviously always frustrating, but it's motivating, Sharapova said". Hitting power shots at Serena just makes her power shots coming back have more pace. You don't need to spend words on his achievements - he is a great champion and someone I have a lot of respect for.

Williams beat Maria Sharapova for an 18th straight time yesterday despite a bout of food poisoning.

Dismissing the idea that this might be her 16th and final appearance at the year's first grand slam - "Hopefully not, unless you know something I don't" she said - Williams spoke of a different approach to her tennis this year.

"She's a great defender and a great girl, and regardless who gets to the final, it will be a good thing", Williams said on court. She broke back to make it level-pegging at 2-2 as the Russian's serve faltered. Czech Berdych had triumphed in their last two meetings at majors but, after a tight opening set, was no match for the clinical Swiss.