Top-seeded Samantha Stosur easily reached the Japan Open quarterfinals with a 6-2, 6-4 victory over Misaki Doi on Thursday.
The U.S. Open champion broke her Japanese opponent three times in the opening set and cruised from there.
The seventh-ranked Australian will next face seventh-seeded Chanelle Scheepers of South Africa, who rallied to beat Kazakh qualifier Yaroslava Shvedova 4-6, 6-3, 7-6 (5).
Second-seeded Marion Bartoli of France also reached the last eight after a 6-1, 6-2 win over American Vania King.
Bartoli will face sixth-seeded Ayumi Morita after the Japanese player beat Eleni Daniilidou of Greece 6-2, 6-3 on the outdoor hard court.