LONDON — All that success finally caught up to Novak Djokovic.

A weary Djokovic finished his spectacular season by losing more matches in three days than he did in the first seven months of the year, earning the top-ranked Serb an early exit in the ATP World Tour Finals.

After winning three Grand Slam titles and seizing the No. 1 ranking from Rafael Nadal before having the last few months derailed by injuries, Djokovic had simply run out of energy coming into the season-ending tournament.

"What is missing ... is that freshness," Djokovic said after losing 3-6, 6-3, 6-3 to fellow Serb Janko Tipsarevic in their final group match. "The will to win, just being on the court, giving 100 percent. I'm not able to do that now because I just have very little left."

Despite finishing the group stage with a 1-2 record, Djokovic would have reached the knockout rounds if Tomas Berdych had lost to David Ferrer in the final round-robin match, but the seventh-seeded Czech rallied from a set and a break down to beat David Ferrer 3-6, 7-5, 6-1 to grab the last semifinal spot.

Ferrer will face Roger Federer in Saturday's first semifinal, before Berdych takes on Jo-Wilfried Tsonga, as the three highest ranked players in the world failed to make it out of the group stage. Second-ranked Rafael Nadal was eliminated after losing to Tsonga on Thursday, while No. 3 Andy Murray pulled out injured following his opening loss to Ferrer.

Djokovic, meanwhile, can start packing his bag for the Maldives, where he plans to join Tipsarevic for a vacation next week as he tries to recharge for next year.