Djokovic, the Wimbledon champion, will finish the season No. 1 for the third time in four years. He is the seventh man to accomplish the feat at least three times.

Djokovic and Federer have swept their groups, and are on course to meet in Sunday's final.

Djokovic will take on Kei Nishikori in the semifinals at the O2 Arena, wile Federer will face his Davis Cup teammate Stan Wawrinka or U.S. Open champion Marin Cilic, who met late Friday.

Djokovic extended his two-year-old indoor winning streak to 30 matches. The two-time defending champion in London, he has lost only nine games this week.

Beside winning his seventh Grand Slam title at the All England Club, Djokovic was also runner-up at the French Open, and won six titles.(KH)

_