World No. 1 and defending champion round winners, while U.S. Open champion Samantha Stosur was an upset victim at the $2.05 million Pan Pacific Open tennis event.
Wozniacki resumed her winning ways in Tokyo with a 6-1, 6-7 (4-7), 6-3 victory over Aussie Jarmila Gajdosova at Ariake Colosseum. The Danish star beat since- retired Russian star Elena Dementieva in last year's finale here.
Meanwhile, the sixth-seeded Stosur succumbed to Russian glamour girl Maria Kirilenko in 6-2, 4-6, 6-4 fashion on Day 3 at this hardcourt tournament.
This marked the Australian Stosur's first action since shocking Serena Williams in the U.S. Open final three weeks ago.
"You never want to go out in the first round after the week I had at the U.S. Open," Stosur said. "It's hard to explain how you could do well at the U.S. Open and then not do well here. I came as prepared as I could."
Stosur beat Kirilenko in the fourth round in New York.
"I just played her a couple of weeks ago, so I knew what to do," Kirilenko said. "Every time you win a Grand Slam, it's tough to win the next tournament."
Three other top stars avoided second-round upsets, as No. 3 Belarusian Victoria Azarenka drilled Romanian Irina-Camelia Begu 6-1, 6-3, No. 4 former U.S. Open and Wimbledon runner-up Vera Zvonareva of Russia handled Bulgarian Tsvetana Pironkova 7-5, 6-0, and No. 5 Wimbledon champ Petra Kvitova of the Czech Republic clobbered qualifier Mandy Minella of Luxembourg 6-2, 6-3.
Ninth-seeded Pole Agnieszka Radwanska overcame German qualifier Angelique Kerber 3-6, 6-3, 6-3; 10th-seeded Chinese Peng Shuai shut down young American Christina McHale 6-0, 6-3; American Vania King upended 11th-seeded Russian Anastasia Pavlyuchenkova 6-4, 7-6 (8-6); and 12th-seeded former No. 1 Ana Ivanovic topped British wild card Laura Robson 7-5, 6-4 in the round of 32.
Additional second-round wins came for 13th-seeded German Julia Goerges, Czechs Iveta Benesova and Klara Zakopalova, and Estonian Kaia Kanepi. Benesova upset 14th-seeded Slovak Dominika Cibulkova 6-4, 6-2, while Zakopalova zipped past 16th-seeded Israeli Shahar Peer 6-3, 6-1, and Kanepi whipped American Coco Vandeweghe 6-2, 6-2.
The first round concluded on Tuesday with six matches, including wins for the aforementioned Peng and Cibulkova. Peng leveled 37-year-old American qualifier Jill Craybas 6-2, 6-0.
Other opening-round wins came for Benesova, McHale, Vandeweghe and Pironkova. The promising 19-year-old McHale bested Austrian Tamira Paszek 7-6 (7-1), 6-3, while the 19-year-old Vandeweghe vaulted past Chinese crowd favorite Zheng Jie 7-6 (7-4), 4-6, 6-2.
No less than six of the top-10 women in the world will take to the courts for third-round action here on Wednesday. Wozniacki will take on Kanepi, while former world No. 1 and 2011 Wimbledon runner-up Maria Sharapova will take on Goerges. Sharapova captured Pan Pacific titles in 2005 and 2009.
Meanwhile, the Wimbledon semifinalist Azarenka will encounter Zakopalova, while Zvonareva will face Benesova, Kvitova will tangle with King, and seventh-seeded Marion Bartoli will be opposed by Peng on Wednesday.
Also seeing action on Day 4 will be eighth-seeded Jelena Jankovic and her fellow Serbian former No. 1 Ivanovic. The 2009 Tokyo runner-up Jankovic should be tested by Radwanska, while the 2007 runner-up Ivanovic should have her hands full with Kirilenko.
The 2011 Pan Pacific champ will collect $360,000.