LONDON - Six-time champion Roger Federer will vie for the title against world No. 1 Novak Djokovic at the ATP World Tour Finals after beating fellow Swiss Stan Wawrinka in the semifinals here on Saturday.

Switzerland's Roger Federer serves to Switzerland's Stan Wawrinka during the men's singles semi-final match on day seven of the ATP World Tour Finals tennis tournament in London on November 21, 2015. [Photo/Agencies]

The 34-year-old fought back from 2-4 down in the first set to win 7-5, 6-3 at London's O2 Arena, reaching the final in the season-ending tournament for the 10th time.

Djokovic, bidding for a fourth successive title, earlier eased past Spaniard Rafael Nadal 6-3, 6-3.

Federer and Djokovic will meet in the final for the third time following their 2012 and 2014 clash, where the Serb won on both occasions.

"It will be the perfect end to the season - if I win," joked Federer. "But otherwise I've still had a good tournament.

"Novak has had a tremendous year and this match will be really difficult. This is the last match of the season.

"I'll give it all I have and leave it on the court," he said.

Djokvic levelled his record against Nadal at 23-23 in career meetings and took his eighth win in their last nine matches.

He said after the match, "I played my best game when it mattered the most and got to the final."

Nadal, who spent two and three-quarter hours winning a meaningless group match over David Ferrer less than 24 hours ago, was totally outplayed.

"He was better than me and he deserved to do what he did during the whole season," said Nadal. "He played just fantastic."