(CNN) -- Serena Williams had to save three match points before beating Caroline Wozniacki of Denmark 6-7 6-3 7-6 in a late-night thriller at the Sydney International on Wednesday.
Williams was delighted to finally wrap up victory over Wozniacki in Sydney.
The top seed faced the match points as Wozniacki served for the match at 6-5 in the decider, but bravely fended them off to force a tiebreaker.
Williams then dominated the tiebreaker seven points to three to wrap up the quarterfinal match in two hours and 40 minutes.
The former world number one had to save four match points before beating Australian Samantha Stosur in her opening match at the WTA event and now faces third seed Elena Dementieva of Russia in the semifinals.
Olympic champion Dementieva beat sixth seed Agnieszka Radwanska of Poland 6-2 5-7 6-4 in an earlier match at the Ken Rosewall Arena.
Russian Dementiava was detained for two hours and 43 minutes but second-seeded compatriot Dinara Safina was an easier winner over Alize Cornet of France. Safina won 6-3 6-4 as Cornet struggled in the hot conditions and plays Ai Sugiyama of Japan in the last four.
Sugiyama received a walkover in the quarterfinals as former U.S. Open champion Svetlana Kuznetsova withdrew with an abdominal strain. Kuznetsova will have a fitness test later this week before deciding whether to play in next week's Australian Open.