Serena Williams ensured the number one raking with her second-round win
Serena Williams, the world number one in waiting, went out of the China Open to Nadia Petrova in round three.
The American, who will take the top ranking from Dinara Safina next week after the Russian lost early in Beijing, went down 6-4 3-6 7-6 (7-5).
Petrova benefited from a dubious call on match point after seeing a 5-0 lead disappear in the tie-break. She will play Shuai Peng in the last eight.
In the men's event, world number two Rafael Nadal beat James Blake.
Williams praised her 27-year-old opponent and said: "I ran into a girl today who has never played so good in her life.
"I don't feel like I ever got into high gear ... I felt like in the second set I got one break and then I just made sure I held serve so I could go to a third set."
Spanish left-hander, Nadal, 23, came through 7-5 6-7 (4-7) 6-3 at the Olympic tennis centre in Beijing and will face Marat Safin in the last eight.
Nadal, who beat Marcos Baghdatis on Tuesday, was playing only his second competitive match since the US Open because of an abdominal strain and was made to work hard by Blake.
"Winning in three sets always gives you confidence but today what really gives me confidence is how I played," said the Spaniard.
"I felt I played really well all the match, one of my best matches since the injury of the knee.
"He's a very good player, I think he has one of the best returns of any player I have played."
Safin enjoyed a surprise 6-3 6-4 win over seventh seed Fernando Gonzalez, while Ivan Ljubicic of Croatia defeated Poland's Lukasz Kubot 7-6 (8-6) 4-6 6-4.
Nadal is making his way back after an abdominal injury
Safin, 29, insisted he would not reconsider his decision to retire at the end of the year despite one of his best wins of the year.
"I don't think today's match is going to be the key to my deciding to play another year, definitely not," Safin said.
"It's easy to play when you have nothing to lose, no points to defend, so you have no pressure at all so you can just play, just go for it.
"If I was playing and had to defend something, it would be a different matter. I would get nervous at some point."
In the women's tournament, 12th seed Agnieszka Radwanska beat Maria Jose Martinez Sanchez 4-6 6-4 6-2, and 14th seed Marion Bartoli beat Zhang Shuai - conqueror of Dinara Safina - 6-1 6-4 to reach the quarter-finals.
Seventh seed Vera Zvonareva defeated 10th seed Flavia Pennetta 6-3 5-7 7-5.