London, England (SportsNetwork.com) - Novak Djokovic will face Roger Federer in Sunday's final at the ATP World Tour Finals.

Djokovic clinched the year-end No. 1 ranking on Friday after completing round- robin play with a perfect 3-0 mark, then went out Saturday and claimed a 6-1, 3-6, 6-0 semifinal win over Kei Nishikori to reach the final at the season- ending event for the third straight year.

The 27-year-old Serb has won this tournament each of the last two years and first captured the title in 2008. He will try to become the first player since Ivan Lendl from 1985-87 to win the championship three straight years.

Federer saved four match points and came back from the brink of defeat to beat his Swiss compatriot Stan Wawrinka, the third seed, 4-6, 7-5, 7-6 (8-6) to reach a ninth final at the ATP Finals. Federer improved to 15-2 lifetime against his Swiss friend.

The 33-year-old Federer, who also went undefeated in round-robin play, is a six-time winner of this event. He won it in back-to-back years three times (2003-04, 2006-07, 2010-11).

Djokovic dropped just nine games in his three round-robin matches and ripped through the first set Saturday in just 23 minutes. Nishikori, who stunned the Wimbledon champion in the semifinals at the U.S. Open, rallied in the second set with a pair of breaks to force a third.

However, the final set was all Djokovic. He broke serve to start the set and never wavered, winning all six games to finish the match in 87 minutes and run his indoor winning streak to 31 straight matches.

Federer leads Djokovic 19-17 in their all-time series.

Nishikori had a banner year, becoming the first Asian player to reach the season-ending event. He won four titles in 2014 and reached two other finals, including his first Grand Slam championship match -- a loss to Marin Cilic at the U.S. Open finale in September.

Wawrinka opened the 2014 season with a victory in Chennai and a first Grand Slam title at the Australian Open. In Monte-Carlo in April, Wawrinka clinched the first ATP Masters 1000 title of his career.