In her second-round match, Petrova was beaten by unseeded Nathalie Dechy of France, 6-4, 6-3.
In other matches, 17-year-old qualifier Agnieszka Radwanska of Poland stunned seven-time Grand Slam champion Venus Williams, 6-3, 6-0; fifth-seeded Francesca Schiavone of Italy beat unseeded Roberta Vinci of Italy, 6-2, 6-1; and unseeded Alona Bondarenko of Ukraine beat Katarina Srebotnik of Slovakia, 4-6, 6-4, 6-3.
Williams aggravated her left wrist injury during the match.
In the quarterfinals on Friday, it will be No. 1 Elena Dementieva of Russia against unseeded Agnieszka Radwanska of Poland; third-seeded Patty Schnyder of Switzerland against Schiavone; No. 4 Dinara Safina of Russia plays Kveta Peschke of the Czech Republic; and Bondarenko will play Dechy.