Mattias Karen

AP Sports Writer

LONDON — Novak Djokovic reached the semifinals of the ATP World Tour Finals by extending his dominance over Tomas Berdych, beating the Czech player 6-3, 7-5 on Thursday in their last round-robin match.

Djokovic only needed to win a set to secure a place in the last four because of the season-ending tournament’s tiebreaker rules and made sure of that after breaking for a 5-3 lead in the first. The Serbian No. 1 wasn’t done, though, breaking for 6-5 in the second before serving out the match and improving his career record against Berdych to 21-2.

He has beaten the Czech five times in the last six years at the ATP finals.

Earlier, Roger Federer clinched first place in the group by beating Kei Nishikori 7-5, 4-6, 6-4 to finish the round robin stage unbeaten.