Top-ranked Caroline Wozniacki defeated 2006 champion Nadia Petrova of Russia 6-3, 6-2 Wednesday to reach the quarterfinals of the Qatar Ladies Open.
The Dane joins No. 2 Vera Zvonareva and No. 5 Jelena Jankovic as the remaining seeded players in the tournament. Zvonareva downed Dominika Cibulkova of Slovakia 6-1, 6-2, and Jankovic defeated Sania Mirza of India 6-0, 6-1.
Wozniacki will play Flavia Pennetta of Italy, who earned a 4-6, 6-3, 6-4 win over Lucie Safarova of the Czech Republic.
''There's a lot of good players here, so it's not easy to win,'' Wozniacki said. ''It's not going to be easy tomorrow, but I'm looking forward to it.''
Earlier, seeded players Francesca Schiavone, Li Na and Shahar Peer lost in straights sets. Unseeded Daniela Hantuchova rallied past Vera Dushevina of Russia 4-6, 6-2, 6-4.
The third-seeded Schiavone lost 7-5, 6-3 to Peng Shuai of China. Fourth-seeded Li was beaten 6-2, 6-1 by Klara Zakopalova of the Czech Republic and eighth-seeded Peer went down 6-1, 6-0 to Marion Bartoli of France.
Peng broke Schiavone twice in each set and will play Bartoli in the quarterfinals.
Schiavone struggled with her serve, hitting five double-faults.
''I was not confident. I could not do too great,'' she said. ''For me to go out first round or third round is not the problem. I missed a lot of easy balls. I should take some days off perhaps, but there is no time.''
Bartoli had three break points in the only game Peer won.
''Shahar has dominated me in the past, so it was nice to get a win against her,'' said Bartoli, who improved to 3-7 against the Israeli.
