Novak Djokovic of Serbia celebrates with the trophy after winning the men's single's final against Roger Federer of Switzerland at the ATP World Tour Finals at the O2 Arena in London, Britain, Nov 22, 2015. Djokovic won 2-0. [Photo/Xinhua]

LONDON - World No 1 Novak Djokovic capped a perfect season as he beat six-time champion Roger Federer to win a record fourth straight ATP World Tour Finals title at London's O2 Arena on Sunday.

The 28-year-old Serb, who lost to Federer in the group stage, broke the Swiss three times to win 6-3, 6-4 in just 80 minutes, levelling their record with the 17-time Grand Slam winner at 22-22.

It was Djokovic's 11th title of the season, including three Grand Slam trophies. He played 88 matches in the season and won 82 of them.

Djokovic, who won the event for the first in 2008, has now collected the season finale five times and surpassed Ivan Lendl's 1987 feat.

"I'm very proud for achievement," Djokovic said. "This season could not have been better. It's been the best of my life."

Federer said: "It is never fun on the not winning side, but it is better than not playing at all like last year. This week was great, there were some crazy points tonight, but like plenty of times this year Novak deserved it."

"With the wins that I had this season and throughout my career, especially in the last five years, I put myself in a very good position, knowing that I made a lot of records and history," said Djokovic.

"I'm convinced with this dedication to the sport, I can achieve more. How much, I don't know. I don't have a sense of urgency. I don't chase anything. I just try to be in the moment and see where it takes me."