Novak Djokovic's [Images] Australian Open [Images] defence ended in a whimper Tuesday when he retired from his quarter-final against Andy Roddick [Images] because of cramping.

The Serbian was trailling Roddick 6-7, 6-4, 6-2, 2-1 on a baking hot day at Melbourne Park when he threw in the towel, becoming the first Grand Slam champion in a decade to quit while defending his title.

"Well, the main reason is cramping and soreness in the whole body," Djokovic said. "I think the people could see that I was struggling with movement.

"(I) really tried my best but sometimes you can't fight against your own body."

There were no indications anything was wrong with Djokovic until he called for a 10-minute medical timeout when he fell behind in the third set.

He slung a bag of ice around his neck to try and cool down as the temperature climbed to 36 degrees Celsius and asked the trainer to massage his legs, neck and shoulders.

"I didn't have any big pains in any particular muscles or parts of the body. It was general soreness," he explained.

Tuesday's episode was the third time in less than three years Djokovic has quit while losing in the latter stages of a grand slam.

He surrendered during the quarter-finals of the 2006 French Open after losing the first two sets to Rafa Nadal then hoisted up the white flag again during the 2007 semi-finals at Wimbledon [Images], also against Nadal.

'SOME RETIREMENTS'

"I did have some retirements but I always retired with a reason. Whenever I retired, I retired because I felt I cannot go on... that's the only reason," he growled.

"There is absolutely no question about whether I have motivation and will and desire to continue the match and defend my title.

"There is absolutely no doubt that I have it in me. My mind wanted me to continue."

Djokovic said he had asked the tournament organisers to schedule his match at night so he could avoid the worst of the heat but his request fell on deaf ears.

Djokovic's fourth-round win over Marcos Baghdatis [Images] was played at night but organisers decided to let Roger Federer [Images] and Juan Martin del Potro play the evening match on Tuesday.

The 21-year-old Djokovic did concede that he was considering changing his preparations for the Australian Open next year after a rushed build-up this time.

Djokovic decided to party in Belgrade on New Year's Eve rather than fly to Australia [Images] early to adjust to the hotter weather.

He was knocked out in the first-round of the Brisbane International by Latvian Ernests Gulbis after playing a leisurely round of golf the day before the match instead of practising.

The world number three was thrown a lifeline and given wildcard into the Sydney International but bowed out in the semi-finals.

"You learn from your mistakes. Obviously I might have changed a little bit this year," Djokovic said.

"I stayed at home for New Year's Eve after a long time but I think I had a good preparation... not a really long, but a good one.

"We tried to improvise as much as we can."

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