The top-ranked Roddick fell in five sets to Russian Marat Safin, 2-6, 6-3, 7-5, 6-7 (0), 6-4, in men's quarter-final play.
With the defeat, Roddick will lose his No. 1 world ranking to either Switzerland's Roger Federer or Spain's Juan Carlos Ferrero, who both play in quarter-final matches Wednesday.
"No one can take away from me the fact that I was there and that I did have it," Roddick said of his spot atop the men's rankings."It's going to be jumping around, I think, a little bit this year."
Russia's Marat Safin upset American Andy Roddick at the Australian Open on Tuesday.(AP Photo/Steve Holland)
Safin, who celebrated his 24th birthday Wednesday, is trying to claw his way back among tennis' elite after missing most of last year due to injury.
"I'm back: That's the most important thing," said the unseeded Safin, who will meet four-time Australian Open champion Andre Agassi in the semifinals.
"I enjoyed my life so much I started to miss tennis," added Safin. "That's why I'm playing so good maybe, because I was making a great life outside of the court."
Agassi advanced to the semis when fellow quarter-finalist Sebastien Grosjean of France retired in the second set with a groin injury.
Agassi, seeded fourth, led 6-2, 2-0 when the Frenchman folded, thereby extending his winning streak at Melbourne to 26.
Meanwhile, Nestor and Bahamian doubles partner Mark Knowles were stunned 7-6, 6-7, 6-3 by the tandem of Gaston Etlis and Martin Rodriguez in Tuesday's quarter-final at Melbourne.
Nestor, who hails from Toronto, and Knowles, the men's doubles champions in 2002, were seeded fourth and seeking a third straight appearance in the final.
Moreover, they took five of six meetings from the ninth-ranked Argentines in 2003.
In women's singles, the fourth-seeded Amelie Mauresmo of France was forced to withdraw prior to her quarter-final match because of a torn back muscle.
Mauresmo suffered the injury lunging forward to make a backhand volley in Sunday's 7-5, 7-5 victory over Alicia Molik.
"As soon as she went up to the net to volley, it was like a knife thrust in her back," said Loic Courteau, Mauresmo's coach.
Mauresmo was teary-eyed after failing to last more than 10 minutes into Tuesday's practice.
"I wanted to try this morning and have a little hit and see how I felt," she explained. "I have pain.
"I have to withdraw from this tournament. When I hit some shots, I can feel really strong pain.
Mauresmo has 10 WTA titles on her resume, but no grand slams.
"I was playing some good tennis and I had some opportunities in this tournament," Mauresmo said. "I always play well here.
"But that's just the way it is. There's nothing to do about it."
Mauresmo's withdrawal vaulted No. 32 Fabiola Zuluaga into the semifinals. Zuluaga is the first-ever Columbian female to reach the final four of a grand slam.
Her opponent in the semis is the top-seeded and defending champion Justine Henin-Hardene, a 7-5, 6-3 victor over No. 5 Lindsay Davenport of the United States.
with files from CP Online
