World No. 1 Novak Djokovic failed to show his sharpness at the ATP World Tour Finals as he suffered two losses in the group stage. The Serbian admitted on Friday that he was short of the freshness at the moment.

Djokovic, 24, took the first set 6-3 while against countryman Janko Tipsarevic but lost the following two 3-6 and 3-6 to the world No 9. [Photo/qq.com]

Djokovic, 24, took the first set 6-3 while against countryman Janko Tipsarevic but lost the following two 3-6 and 3-6 to the world No 9.

Two days ago, Djokovic was defeated by Spain's David Ferrer, whom then earned a semifinal berth with two straight set wins.

Coming to the season finale with 10 titles including three from the Grand Slams this season, Djokovic dominated the tour with a 69- 4 match record.

When he struggled to beat Tomas Berdych in the opening match, then lost the following two in London, a journalist even said, "We 're not used to that."

"Freshness," Djokovic told what he was missing now. "The body says that it's overloaded. It's been too much this year. Obviously mentally I feel a little bit drained as well. I just don't have that freshness in my mind for the matches and I don't have these dynamic that I had in all 10 months of the year."

The world No. 2 Rafael Nadal said he's lost a little bit of his passion for tennis on Thursday and Djokovic said he could understand the Spaniard.

"I think you have those days where you don't feel like playing, you don't feel like practising. There are tournaments, especially the ones towards the end of the year where you don't feel as hundred percent fresh mentally, physically, emotionally. Obviously that's why he felt that way," said Djokovic.

"I understand him. Because I can say we are more or less in a similar situation," he added.

However, Djokovic insisted that nothing could really ruin his 2011 season. "I will always remember this year as the best of my life. I just want to prepare well for 2012."