BEIJING (AFP) Serena Williams was knocked out of the WTA/ATP event in a third set tiebreak. World number two Williams battled back several times but was unable to overcome Russian 13th seed Nadia Petrova, who fired 14 aces in a three-set victory, 6-4, 3-6, 7-6 (7/5). The loss means that the top three seeds Dinara Safina, Williams and her sister Venus have now been knocked out of the tournament before the quarterfinals. The 28-year-old Williams looked lethargic in the first set, with her ground strokes sailing long and her serve broken twice to hand the 27-year-old Russian the early lead. But the American bounced back in the second, putting a bit more pace on her shots and dictating play from the backcourt to gain a break late in the set and even the match. In the deciding third set, Williams missed a golden opportunity to pull ahead at 4-4, blowing three break points on Petrovas serve. But she cranked up her serve to send it to a tiebreak. After Petrova took an early 5-0 lead, Williams battled back one final time to 5-6 before the Russian closed it out. I dont feel like I ever got in high gear. I felt like she was controlling the whole match, Williams said. I ran into a girl today who has never played so good in her life.... I had some opportunities that I let slip through my fingers. I tried to do well tonight but it didnt work out so well, Williams said. Despite the loss, Williams an 11-time Grand Slam winner will nevertheless take over the number one ranking from Safina when the new WTA list is issued on Monday. In other third round matches on the womens side of the 6.6-million-dollar event, seventh seed Vera Zvonareva of Russia, Polish 12th seed Agnieszka Radwanska and 14th seed Marion Bartoli of France all advanced.