LONDON - World No. 1 Novak Djokovic took another step towards winning a fourth successive title at the ATP World Tour Finals after beating Tomas Berdych in their final group match to reach the semifinals here on Thursday.

Djokovic will next face Rafael Nadal, who has secured the top position in the other group.

The 28-year-old Serb, who required just one set to qualify, scored a straight-set victory over the sixth seeded Berdych 6-3, 7-5.

Federer, who snapped Djokovic's 23-match winning streak two days ago, had already won the group but earlier maintained his 100 percent record with a 7-5, 4-6, 6-4 win over Kei Nishikori of Japan.

The six-time winner will meet the winner of the other match on Friday between Andy Murray and Swiss No. 2 Stan Wawrinka.

"Rafa has another match tomorrow and I'm going to watch that a little bit with my team and prepare," said Djokovic.

"Hopefully I'll be able to perform at my best because that's what's needed to win against him."