OSAKA, Japan -- Defending champion Samantha Stosur of Australia advanced to the quarterfinals of the Japan Women's Open on Wednesday with a 6-0, 6-3 win over Japan's Junri Namigata.
Tamarine Tanasugarn outlasted Coco Vandeweghe of the United States in a three-hour marathon 7-5, 5-7, 6-4.
The top-seeded Stosur, whose win last year was her first WTA singles title, needed only 63 minutes to improve to 7-0 at the event.
Stosur won the first eight games of the match before Namigata got on the board.
Second-seeded Marion Bartoli of France joined Stosur in the quarterfinals with a 6-2, 6-2 win over Swiss player Stefanie Voegele.
Maria Kirilenko of Russia retired after dropping the first set 6-4 to Chang Kai-chen of Taiwan.