Federer, Djokovic Prevail at World Tour Tennis Finals

Roger Federer and Novak Djokovic prevailed on Thursday to join Rafael Nadal in what is shaping up to be a fantastic four this weekend at the World Tour Finals.

Federer was already assured of a 13th semifinal spot in 14 years at the season finale, so it was perhaps only natural his level would drop off as he squeaked past an inspired Kei Nishikori 7-5, 4-6, 6-4 in a match full of twists and turns.

The victory confirmed Federer's progress as group leader with Djokovic simply having to avoid losing in straight sets against Tomas Berdych to qualify in second spot.

The world No.1 only needed 42 minutes to make sure of that, breaking Berdych for the second time to win the opening set before wrapping up a 6-3, 7-5 victory.

He now renews his rivalry with Nadal, who leads their tightly-contested head-to-head 23-22, though Djokovic has won all three meetings between them this season including the Beijing final and twice on clay in the Monte Carlo semis and Roland Garros quarterfinals.

"It's a fact that he's [Nadal] been playing better and he's been raising his level ever since U.S. Open," said Djokovic in his post-match press conference.

"Already in China, playing finals in Beijing, semifinals in Shanghai, you can feel that he's starting to get comfortable on the court, start to play better. The first couple of matches he played here against [Stan] Wawrinka and [Andy] Murray showed that he feels more confident, that he's starting to miss less, serve efficiently, use his forehand much better.

"I know that, I've been watching. I know what is expecting me. We played so many times. I'm going to get ready for that one and hopefully I'll be able to play at my best."

For Djokovic, it was important to bounce back from Tuesday's shock loss to Federer, which snapped streaks of 38 consecutive indoor wins, 23 overall since August 23 and 15 straight at the World Tour Finals.