Osaka, Japan: Samantha Stosur beat Swiss qualifier Belinda Bencic 6-4, 6-2 here on Wednesday and became the top remaining seed after Wimbledon runner-up Sabine Lisicki backed off due to injury.
No. 2-seeded Lisicki withdrew because of injury in her left hip, and ruled herself out from her planned second-round match with Slovenia's Polana Hercog. Hercog moves up to a quarterfinal with local wild card Kurumi Nara.
Samantha, the No. 3 seed, attained her first quarterfinals since her title run in Carlsbad in August. She lost her serve twice but ruined Bencic five times at Utsobu Park and will next face either Kimiko Date-Krumm or Misaki Doi in the last eight.
Stosur won in Osaka in 2009 and was runner-up in 2011 and a semifinalist in 2012.
In other second-round matches, Nara beat eighth-seeded Monica Puig of Puerto Rico 7-5, 7-6 (4), and fifth-seeded Eugenie Bouchard of Canada overpowered Luksika Kumkhum of Thailand 6-2, 6-2.
Czech qualifier Barbora Zahlavova Strycova defeated Vania King of the United States for the second time this year, 2-6, 6-3, 6-1, and will meet Bouchard next.