Martina Hingis beat Daniela Hantuchova 7-5, 6-4 to reach the quarterfinals of the Rogers Cup.
The former top-ranked player will face fourth-seeded Svetlana Kuznetsova, who defeated Ai Sugiyama of Japan 6-2, 7-6 (6).
The seventh-seeded Hingis fought back from 0-40 to break the Slovak's serve for a 6-5 lead and needed four set points to win the first set.
Hingis, who won the tournament in 1999 and 2000, returned to the WTA Tour this season after three years of nursing foot and ankle injuries and looks to be returning to form.
"It seems that all week people have been withdrawing, but in my section (of the draw), no one wants to retire," Hingis said with a laugh. "The main thing is there's still eight great players out there."
"I've had some great matches with Kuznetsova and I know I'll have to come out with my best."
Katarina Srebotnik defeated Canada's Stephanie Dubois 6-3 6-2 to advance to the final eight.
Australian qualfier Nicole Pratt advanced on a walkover when Nicole Vaidisova of the Czech Republic withdrew because of a strained right shoulder. Ana Ivanovic advanced when fellow Serbian Jelena Jankovic withdrew with an undisclosed injury.
Vaidisova said she would rehab her injury and try to be ready for the US Open in less than two weeks.
"I'm not injured, I'm just preventing it from getting injured," said Vaidisova.