Newly crowned World Number One Serena Williams suffered a shocking third round defeat at the hands of Russian Nadia Petrova at the 2009 China Open, being played here in Bieijing, China.

Williams, who regained the top spot in WTA rankings with a win over Ekaterina Makarova in the previous round, looked rusty from the very start of the match and got broken early on. As the match progressed, Williams found the rhythm she was looking for, to level the tussle one set a piece.

In the decider both players fought for every single point and as a result the match got pushed into a deciding tie-break where Petrova raced to a 5-2 lead before Williams won the next two points on Petrova's serve to get back in the contest. However, on her third match point, the Russian closed the 6-4, 3-6, 7-6(5) encounter after a struggle of two hours and 19 minutes.

Earlier in the day, Polish teenager Agnieszka Radwanska came back from the brink of defeat to beat Spaniard Maria Jose Martinez Sanchez to reach the quarterfinals of the event.

Martinez Sanchez opened the match well and pocketed two breaks to wrap up the opening set 6-4. As the match progressed she raced to a 4-0 lead in the second before Radwanska reeled off seven games in a row to level the match. As the unforced errors kept coming from the Spaniard's racquet, Radwanska completed the 4-6, 6-4, 6-2 win in two hours and 17 minutes of play.

Indian Wells champion Vera Zvonareva also dug deep before rallying past Italian Flavia Pennetta 6-3, 5-7, 7-5 in a see saw match that lasted two hours and 33 minutes in play.

In the day's first match, Frenchwoman Marion Bartoli beat Dinara Safina's conqueror Shuai Zhang in straight sets to reach the last eight. Bartoli, who beat American Venus Williams in Stanford final during the US Open series, looked sharp from the very beginning and completed the 6-1, 6-4 win in one hour and 32 minutes.