Top-ranked Serena Williams advanced to the Rogers Cup quarterfinals Thursday night, beating 16th-seeded Andrea Petkovic of Germany 6-3, 6-2.
"I think I served better," Williams said. "It was a big difference. I still think I have a tremendous amount of improvement to do off the ground and everywhere else."
Williams won titles in Toronto titles in 2001, 2011 and 2013. The 21-time Grand Slam singles champion will face Italy's Roberta Vinci, a 6-4, 6-3 winner over Russia's Daria Gavrilova.
Second-seeded Simona Halep of Romania also advanced, outlasting 13th-seeded Angelique Kerber of Germany 6-3, 5-7, 6-4 in hot afternoon conditions.
"I did well in the last game," Halep said. "I said, `I have to win it because I cannot move anymore.'"
Halep will face sixth-seeded Agnieszka Radwanska of Poland, a 6-2, 4-6, 6-4 winner over Alize Cornet of France.
In the late match, fifth-seeded Ana Ivanovic of Serbia defeated Slovenia's Polona Hercog 6-2, 6-3.
Unseeded Belinda Bencic topped Sabine Lisicki 6-1, 1-6, 7-6 (3) to keep her run going. The 20th-ranked player from Switzerland opened the tournament with a victory over slumping Canadian Eugenie Bouchard and followed it with an upset win over fifth-ranked Caroline Wozniacki of Denmark.
Bencic will play Ivanovic.
Also, 15th-seeded Sara Errani of Italy beat Belarus' Victoria Azarenka 7-5, 6-3, and Ukraine's Lesia Tsurenko beat Germany's Carina Witthoeft 6-3, 6-4.
