Melbourne, Jan. 27 : Defending champion Novak Djokovic has quit the Australian Open, retiring from his quarter-final against Andy Roddick on Tuesday.

Djokovic, the No. 3-seed, from Serbia, was trailing the No. 7 seed, from the United States, 6-7 (5-7) 6-4 6-2 2-1 when he quit the match, after two-and-a-half hours, apparently suffering from heat stress.

Melbourne  - Andy Roddick says he's impressed with new ATP boss Adam Helfant, after meeting his fellow American at the Australian Open.

"I actually was lucky enough to have dinner with him the other night. I was pretty impressed," said Roddick. "He didn't come in with kind of this braggadocio attitude of what he's done, whatever. He kind of came in and he had his notepad and his pen, and he asked questions, and he wrote down notes. He didn't come in like a know-it- all."

Melbourne  - One-time Grand Slam winner Andy Roddick renewed his fight to regain relevance in tennis on Monday, beginning his Australian Open campaign with a defeat of Swedish qualifier Bjorn Rehnquist 6-0, 6-2, 6-2.

The number eight US player lifted his lone major honour at the 2003 US Open, then gradually slid into neutral and fell from the discussion when big titles were mentioned.

Melbourne  - Ana Ivanovic led a trio of seeds to opening-day victories Monday at the Australian Open, with Serbia's former number one defeating German Julia Goerges 7-5, 6-3.

Fifth seed Ivanovic was followed into the second round by Russian number seven Vera Zvonareva, a 7-6 (7-2), 6-0 winner over Slovak Magdalena Rybarikova.

French ingenue Alize Cornet, the 15th seed, completed the early sweep against Mariya Koryttseva of the Ukraine 6-3, 6-4.

New York - Andy Roddick will hope to jump-start his stalled tennis as he begins work in 2009 with veteran coach Larry Stefanki.

Former number one Roddick, who withdrew from last week's Masters Cup after rolling an ankle before a match, announced on his website that he and the former mentor to John McEnroe, Marcelo Rios, Yevgeny Kafelnikov, Tim Henman and Fernando Gonzalez will team up within weeks.

Shanghai - Andy Roddick withdrew from the Masters Cup shortly before his match on Wednesday, citing a right ankle injury he suffered during training the day before.

The American, who lost his opening match to Andy Murray, will be replaced in the Red group by Czech Radek Stepanek.

The American dropped his bombshell a few hours before he was due to take to the court against Roger Federer.

"In practise I just went over on it, we tried as much as we could to get it better," he said. "I can't really stop and start very quickly. It's anything when I go kind of over on the outside it hurts.