Top-ranked Caroline Wozniacki beat 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 left 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 hard-fought 4-6, 6-3, 6-4 win over Lucie Safarova of the Czech Republic.
"I just focus on myself and I try to win," said Wozniacki, who broke once in the first set and twice in the second. "There's a lot of good players here, so it's not easy to win. I'm just taking it one day at a time. It's not going to be easy tomorrow, but I'm looking forward to it.
"My serve was quite good, so too the returns. Considering the fact that Nadia serves well, it was important to get my returns right."
Earlier, seeded players Francesca Schiavone, Li Na and Shahar Peer lost in straights sets.
The third-seeded Schiavone lost 7-5, 6-3 to Peng Shuai of China. The fourth-seeded Li was beaten 6-2, 6-1 by Klara Zakopalova of the Czech Republic, and the eighth-seeded Peer went down 6-1, 6-0 to Marion Bartoli of France.
In another match, Daniela Hantuchova rallied to beat Vera Dushevina of Russia 4-6, 6-2, 6-4.
Peng broke Schiavone twice in each set and will play Bartoli in the quarterfinals.
"Playing against Francesca is always difficult, but I was the better player today," Peng said. "She tested me in the first set, but I was more determined."
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.
Sixth-seeded Victoria Azarenka and No. 7 Agnieszka Radwanksa were the other seeded players who bowed out of the tournament.