Vera Zvonareva led the top three seeds into the third round of the San Diego Open on Tuesday with a 6-4, 7-5 win over American Jill Craybas.
Russia's Zvonareva, a two-time Grand Slam finalist, was followed into the third round by second-seeded Andrea Petkovic of Germany and third-seed Agnieszka Radwanska of Poland.
Petkovic, currently ranked 11th but but poised to move into the top 10 next week according to WTA projections, defeated American Alexa Glatch 6-3, 6-4.
Radwanska overcame Britain's Elena Baltacha 6-0, 7-6 (7/4). All three had been given byes to the second round.
Zvonareva arrived in California after claiming a 12th career title in Baku, Azerbaijan, in July.
She said she expected a tough match from Craybas, who won two qualifiers and a first-round match to reach the second-round encounter.
"She got a couple of matches under her belt and got used to the conditions so I knew it was going to be a tough one," Zvonareva said. "I don't expect myself to play my best tennis in the first match of the tournament."
Sixth seed Dominika Cibulkova was forced to withdrew from the event with a left abdominal muscle strain.
The Slovakian had pulled out of her semi-final match at Stanford on Saturday with the injury, but had hoped to be able to play in San Diego.
"I was really hoping that it would heal fast and I would be able to play," said Cibulkova. "Unfortunately it's still a problem and I have to withdraw."
In first-round action, Japan's 40-year-old wonder woman Kimiko Date-Krumm beat newlywed Argentinian Gisela Dulko 7-5, 6-0.
Date-Krumm won the event in 1996, not long before she retired and spent 11 years out of the game.
Her victory in just under 90 minutes, with six breaks of the distracted Dulko, got Date-Krumm off to a much more promising start after she lost in qualifying here last year.
Date-Krumm, who took five-time champion Venus Williams to three sets in the second round at Wimbledon in June, said she had some luck in her victory over Dulko, who married Real Madrid footballer Fernando Gago a few weeks ago.
She said her appearance in San Diego has not prompted her to reflect on her title run here a decade and a half earlier.
"It was a long time ago. I had a lot of confidence then," she said. "Of course I was much younger and all of the muscles and the shots -- they were better then than now. But I'm enjoying my tennis more now than I did back then."
Italy's Alberta Brianti defeated 10th-seeded compatriot Flavia Pennetta 1-6, 6-2, 6-2 while Germany's Wimbledon semi-finalist Sabine Lisicki, the number 12, hammered Greta Arn of Hungary 6-0, 6-2.
"I didn't have much time to adapt, I only got here two days ago," said 25th-ranked Lisicki a semi-finalist last weekend in Stanford against Serena Williams. "I'm happy with how I played."
Russian 11th seed Maria Kirilenko beat Rebecca Marino 6-3, 6-2 with the Canadian troubled by back pain and needing a medical timeout but saying she will be fine for Toronto next week.
New Zealand's Marina Erakovic upset Russian number 14 Elena Vesnina 6-1, 6-2. Austrian Tamira Paszek, a Wimbledon quarter-finalist, rallied to get past Romanian Simona Halep 0-6, 6-4, 7-5.