Number 14 seed Daniela Hantuchova was the other seed to fall on Wednesday, losing 7-5, 4-6, 6-2 to doubles partner Ai Sugiyama of Japan, while fifth seed Patty Schnyder survived a 6-4, 6-7, 6-1 match against Czech Kveta Peschke.

Playing with a right elbow strain, Petrova was unable to impose herself against Mirza, who dictated play during the match.

Mirza, who had to qualify for the main draw, went all out with her forehand returns and was never threatened by the 2005 French Open semifinalist.

Mirza said nothing was easy playing a top-10 ranked player.

"I knew if I relaxed for a second she would have jumped on me," said Mirza, who will face Japan's Akikio Morigami in the next round. "I had a game plan in my mind and I'm glad I was able to do what I needed to.

"I believed I could do it, but I always knew that everyone is beatable."

Ranked a career high 59, Mirza is almost sure to crack the top 50 in the next two weeks, achieving the goal she had set herself at the beginning of the year.

She has already won her first career title, at Hyderabad beating four seeds on the way, beat the then world number seven Svetlana Kuznetsova in Dubai and made two other quarterfinals.

"A lot has happened since January," the 18-year-old added.

"I started this season losing in the second round of qualifying of Tasmania.

"I didn't expect so much to happen so soon, but I'm not complaining."

French Open finalist Mary Pierce, playing her first match on hard courts since March, thrashed Germany's Anna-Lena Groenefeld, who was never able to establish her big serve or whipping return.

"I didn't expect to play that well because in your first match on a surface, you don't know what's going to happen," Pierce said of the 6-1, 6-1 victory.

"I was really happy today, especially with the first set. I took her seriously. From first point of match, I was ready to play."

In other matches, ninth-ranked Elena Likhovtseva recovered from a set down to beat Israel's Shahar Peer 0-6, 6-2, 6-4, while 10th seed Nathalie Dechy also came from a set down to beat Argentine Gisela Dulko 4-6, 7-5, 7-6.

Russia's 16th-ranked Dinara Safina also recovered from losing the first set to love to beat compatriot Alina Jidkova 0-6, 6-1, 6-0, while Italy's 17th seed Francesca Schiavone beat Anastassia Rodionova 6-2, 6-2 and Bulgaria's Sesil Karatantcheva beat Lisa Raymond of the US 7-6, 6-4.