Novak Djokovic says it's unfair to discredit his breakthrough Australian Open triumph amid intensifying debate over Roger Federer's health and fitness at the season's opening grand slam.

Unsubstantiated rumours have surfaced that Federer - who was forced to withdraw from the Kooyong Classic the week before the Open with food poisoning - shed three kilograms battling fever in the lead-up to his flat semi-final loss to Djokovic at Melbourne Park.

One close source claimed Federer "looked real crook, really bad" after his first practice session before the Open and observers also questioned whether the top seed's illness contributed to his dramatic five-set escape against Serbian No.2 Janko Tipsarevic in the third-round - and subsequent loss to Djokovic six days later.

But as he basked in the glory of landing his and Serbia's first-ever slam and set his sights on Federer's world No.1 ranking, Djokovic refused to believe his breakthrough success on Sunday was anything other than further evidence he was closing the gap on the Swiss master.

The 20-year-old felt he simply outplayed the two-time defending champion after "taking the positives and negatives" from his tight three-set loss to Federer in the US Open final four months earlier.

"You could see everything on the court. He didn't seem at all like having a fever or something. No, I don't have any comments on that," Djokovic said.

"I think I was the better player on the court and absolutely deserved to win.

"I was mentally stronger (than in New York) and I played with more patience in crucial moments and I think that made the difference."

For his part, the classy Federer said Djokovic had been too good on the night but added somewhat mysteriously: "I mean, considering, you know, my illness, I'm sort of happy with the result here."

Djokovic trailed Federer 5-1 head-to-head before last Friday, but his victory over the 12-time grand slam winner two weeks before last year's US Open suggested he was a force to be reckoned with.

The world No.3 said in their earlier meetings he had just wanted "to prove that I'm a good tennis player".

"But now things have changed," Djokovic said.

"Now I believe more in myself and now I get to the matches with more belief that I can win and that I want to win.

"There is a slight difference and he feels it and I feel it much more, and I'm very happy that I managed to beat the best player in the world in straight sets."

Djokovic admitted he now must reassess, having already achieved his season goal of winning his first major, and that overtaking world No.2 Rafael Nadal and Federer to finish as the year-end No.1 was "even possible".

Significantly, Federer and Nadal both have more rankings points to defend in 2008 after splitting last year's French Open and Wimbledon finals and Federer reigning in New York, where Nadal made the last 16.

Djokovic, a semi-finalist or better at the past four majors, said if he can maintain consistency, reining in Federer and Nadal wasn't out of the equation.

"I think I have enough quality to do it," Djokovic said.

"On the rankings, you see that points-wise they are not so far away and not so dominant.

"So now I look at things in a different way.

"As a grand slam winner now, people now expect me to get further and to challenge those two guys for the first two places in the world.

"That's still a question. I always believe that I can reach everything and I think that's even possible.

"We'll see what happens. But now I feel much more better, much more confident."

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