Two-time defending champion Serena Williams needed a third-set tiebreaker on Saturday to beat Caroline Wozniacki and advance to the WTA Finals title match in Singapore.

The world No.1 posted her fourth win of the year against the eighth-ranked Danish player 2-6 6-3 7-6 (8-6).

Williams remains on course for a third-straight title in the season-ending championships.

Wozniacki served for the match at 5-4 in the third set but Williams broke back and prevailed in the tiebreaker on her third match point after trailing 4-2.

The American will face No.4 Simona Halep of Romania or Poland’s No.6 Agnieszka Radwanska in Sunday’s final.

Williams has won 10 of 11 matches against Wozniacki, including this year’s US Open final and two other 2014 matches in which she recovered from a set down.