Andre Agassi paid tribute to Roger Federer after suffering a comprehensive defeat at the hands of the defending champion in the Australian Open.

Federer extended his winning streak to 26 matches with a surprisingly one-sided 6-3 6-4 6-4 quarter-final victory over a subdued Agassi on Rod Laver Arena.

The world number one and top seed needed just one hour and 39 minutes to book a semi-final clash with Marat Safin, a repeat of last year's final.

It was only the second time Agassi had been beaten in straight sets in Melbourne, the four-time champion never in contention against Federer, who fired down 22 aces - as many as he managed in total in the previous four rounds.

Federer has now won his last five matches against Agassi, his last 24 against players in the world's top 10, and not lost a match since the second round of the Olympics in Athens.

Asked to rate his opponent's current level of play, Agassi admitted: ''Way better than mine tonight, way better than mine. That's a hard game to stop for many reasons. I certainly didn't do anything to make a dent in that.

''He does everything well and a lot of things great.

"His movement is probably the most underrated part of his game, and that's right up there with the best of them. His forehand is one of the biggest. His serve is very accurate.

''I dropped my serve early in each set. I mean, you're just asking for pain. And I felt like I got what I deserved in that regard.

''I was disappointed with not executing good shots early in the sets to give myself a chance to settle into the match. I never got my teeth into it and when I don't get my teeth into a match, I can look pretty ordinary.

''It's disappointing. I've spent a lot of years coming down here and having some real memorable matches and leaving with the trophy.

"I wanted tonight to be memorable but it's one I'd probably prefer to forget.

''At the net I told him, 'Too good and good luck'. He said he enjoyed playing against me and hopes that happens more. I said, 'That makes one of us'.''

Federer was almost equally convincing against Safin in the final 12 months ago, but expects a tougher contest in the semi-final against the in-form fourth seed.

''I'm really looking forward to the contest with Safin,'' he added.

''I have the feeling he's playing good again and he had a great finish last year, a good start this year. It's going to be a really hard match.''

Safin had earlier made the most of the cooler conditions under the closed roof of the Rod Laver Arena.

Soaring temperatures in Melbourne meant the roof was closed for Safin's match with Dominik Hrbaty, although the women's quarter-finalists had not been so lucky earlier in the day.

And Safin clearly enjoyed the perfect indoor climate as he disposed of Hrbaty 6-2 6-4 6-2 in just 90 minutes.

Serena Williams was quick to hit back at suggestions she and sister Venus were in decline after easing into the Australian Open semi-finals.

Williams thrashed France's Amelie Mauresmo 6-2 6-2 in Melbourne, her ninth win in ten matches against the second seed.

The former world number one will face Maria Sharapova in the semi-finals, a repeat of last year's Wimbledon final won by the Russian teenager.

That defeat meant last year was the first time one of the Williams sisters had failed to win a grand slam since 2000, with four different winners of the four major titles.

It is all a far cry from the time the Williams' dominated women's tennis in a manner previously unheard of. From Wimbledon 2000 to 2003, between them they won nine of the 13 grand slams contested, Venus winning four and Serena five.

However, Venus has not won a grand slam since the 2001 US Open, and crashed out in the quarter-finals here, beaten in straight sets by Australian Alicia Molik.

Rumours persist the sisters care more about their off-court interests than tennis, but Serena pointed to injuries and the death of their sister Yetunde Price in September 2003 as mitigating factors.

Asked if she needed to win the title to prove she and Venus were not in terminal decline, Williams said: ''I don't appreciate that language, to be honest with you.

"I'm tired of not saying anything, but that's not fair. We've been practising really hard.

''We've had some serious injuries. I've had surgery and after surgery I got to the finals of Wimbledon. I don't know too many people that have done that.''

Sharapova overcame the stifling heat and compatriot Svetlana Kuznetsova. Sharapova recovered from losing the first set to record a 4-6 6-2 6-2 victory