MELBOURNE, Jan. 27 (Xinhua) -- American Andy Roddick made his way safely into the Australian Open semifinals for the fourth time, leading defending champion Novak Djokovic 6-7 (3), 6-4, 6-2, 2-1 when the Serbian retired on a sweltering Tuesday in Melbourne.
The Serbian world number three, who broke through for his first Grand Slam win here last year, won the tie-break of the first set, but looked listless in the remaining match under a scorching sun despite asking for a medical timeout.
The first set saw both players hold solid serve, but Roddick, taking advantage of a sluggish serve from Djokovic, broke his opponent four times in the second and third sets to retain the momentum in his favor.
"I think a lot of people expected me to do well here because of the title. Obviously, it's very disappointing. But you have to take the best out of it and be positive. That's where I'm trying to be. There is still a long season in front of me," said Djokovic.
Swiss mogul Roger Federer, struggling with form against Czech Tomas Berdych in a dramatic thriller in the round of 16, finally found his rhythm and destroyed Argentine Juan Martin del Potro 6-3, 6-0, 6-0 in only one hour and 20 minutes.
"You have to ask Roger what happened. I can't do anything in the match. He plays like No. 1 of the world, so that's it," a forlorn del Potro said at the press conference.
Earlier, Russian Vera Zvonareva continued to dominate her head-to-head record against Frenchwoman Marion Bartoli with a runaway 6-3, 6-0 win in the women's singles quarterfinals.
"I don't know what happened, I thought Marion was playing really well in the beginning, but I was able to cut down on my unforced errors and keep a good level of play throughout the rest of the match," said Zvonareva, who now advances to her first Grand Slam singles semifinal.
"I was able to play a very, very clean match today. That's what made the difference."
But No.16 seed Bartoli should have pulled off a strong form which lifted her over world number one Jelena Jankovic in the round of 16. In that match, the Frenchwoman hit as nearly twice as many winners against the Serb.
"I think she played just unbelievably well. She barely misses one ball. I was hitting as hard as I could. She was coming back with some better shots," said Bartoli, who led 3-1 in the opening set.
"Even when she was scrambling, she was putting the ball just ten centimeters from the baseline. It seems like she's reading my game like in the book. It was just too good."
Coming up next for the Russian in the semifinal will be her compatriot Dinara Safina, who withstood a second set challenge to dispose of Australian wildcard Jelena Dokic, a former world number four.
"It was not easy to play, you know, having the whole crowd against. Because when you have the whole crowd on your own behind your back, whenever you do a great shot, they pump you and then it makes you go for more and more," said the Russian, who looks to win her first Grand Slam title.
"Next round I play Vera, and she plays very good. I have to take the time off her and take the balls much earlier. Definitely I will have to be much more aggressive than today," she said of her next match.
"Dream (of winning one Grand Slam) is always there. But, you know, now that it's semifinal. Whatever happens, it happens. I want to go out there and play my game, and let's see who is gonna be stronger that day."