Melbourne: Roger Federer showed why he's the Australian Open's modern-day king with a majestic victory over Juan Martin del Potro, as women's champion Kim Clijsters also reached the semi-finals.

\Federer, a four-time winner at Melbourne Park, was at his regal best in the Melbourne heat as he made light of an expected stiff challenge by del Potro, his conqueror in the 2009 US Open final.

The 16-time grand slam winner from Switzerland, now 30, barely gave the 6ft 6in (198cm) Argentine a look-in and he took it 6-4, 6-3, 6-2 after 1hr 59min of glorious tennis on the centre court.

Federer started like a rocket and broke at the first opportunity, taking the first set in 43 minutes. In the second set, he fought off four break points in a pivotal game nine to go 2-0 up, celebrating with a trademark guttural roar.

Del Potro has returned to 11 in the rankings after serious injury but his head dropped in the third set as Federer closed it out with his thunderous inside-out forehands and classic, one-handed backhand.

The victory put a broad smile on the face of the Swiss, who is aiming to become only the second man to win the Australian Open five times or more after Roy Emerson in the 1960s.

"I'm very happy," Federer said. "I thought it was a great match. It was tough with the sun and shade creeping across the court but I thought we did well. I thought it was a high-quality match."

Federer will next face either his great rival Rafael Nadal or Tomas Berdych, who play later. Top seed Novak Djokovic and world number four Andy Murray are also into the quarter-finals on the other side of the draw.

Meanwhile women's defending champion Clijsters ousted top seed Caroline Wozniacki and ended her controversial reign as world number one with a straight-sets win in the quarter-finals.

Clijsters held off a determined fight-back from the 21-year-old Dane to win 6-3, 7-6 (7/4) in 1hr 45min and set up a semi-final against third seed Victoria Azarenka, who beat Poland's Agnieszka Radwanska.

By failing to reach the last four, Wozniacki is guaranteed to lose her number one ranking to Azarenka, Petra Kvitova or Maria Sharapova when the new standings are released on next Monday.

Wozniacki has occupied the top spot since October 11, 2010, apart from one week last February, but she has faced constant questions over her right to be considered the best women's player, because she has never won a major title.

But the defiant Dane, who lost her only grand slam final to Clijsters at the 2009 US Open, backed herself to bounce back by the end of the year.

"You know, to be honest, I don't really think about it," a defiant Wozniacki said. "I have been there for a long time already. I finished number one two years in a row.

"We are just in January. In the end of the year you see who has played the best, most consistently all year round. I will get it back eventually, so I'm not worried."

Former champion Maria Sharapova and Ekaterina Makarova will contest an all-Russian quarter-final on Wednesday, while Wimbledon title-holder Petra Kvitova plays Sara Errani of Italy.

(Agencies)