Two of this week's top-four seeds -- last year's runner-up Agnieszka Radwanska and Caroline Wozniacki -- and former world No. 1 Venus Williams were among Wednesday's third-round winners at the $2.37 million Pan Pacific Open.
Fresh off her title in Seoul, the former Wimbledon runner-up Radwanska rolled past 16th-seeded Slovak Dominika Cibulkova 6-3, 6-4, while the fourth-seeded former world No. 1 Wozniacki whipped unseeded Slovak Magdalena Rybarikova 6-1, 6-1 on the hardcourts at Ariake Coliseum.
Up next for the 2011 Tokyo titlist Radwanska will be fifth-seeded German Angelique Kerber, while the 2010 Pan Pacific champion Wozniacki will encounter Czech Lucie Safarova in Thursday's quarterfinals.
Radwanska lost to Russian Nadia Petrova in last year's finale in Tokyo.
Meanwhile, the unseeded Williams took out 13th-seeded rising Romanian Simona Halep 4-6, 7-5, 6-3 on Day 4.
"It was a very tough match," Williams said. "She played very well. I don't know how I was able to win the match. I just wanted to stay in Japan longer."
Williams stunned top-seeded and fellow former world No. 1 Victoria Azarenka here on Tuesday.
Her quarterfinal opponent will be promising Canadian Eugenie Bouchard, who bounced sixth-seeded former top-ranked star and 2009 Tokyo runner-up Jelena Jankovic 7-5, 6-2.
In some other round-of-16 action, fifth-seeded German Angelique Kerber handled 11th-seeded former No. 1 and 2007 Pan Pacific runner-up Ana Ivanovic 6-4, 6-2 and Czech Lucie Safarova doused 12th-seeded former U.S. Open champ Samantha Stosur 6-4, 6-4.
Wednesday's schedule featured four former world No. 1 stars.
Also on Wednesday, seventh-seeded former Wimbledon champ Petra Kvitova was scheduled to meet American Madison Keys, but that match was postponed, and 15th-seeded Romanian Sorana Cirstea was leading two-time Grand Slam winner and 2008 Tokyo finalist Svetlana Kuznetsova 4-1 when their match was suspended because of rain.
The 2013 Pan Pacific champ will earn $426,000.