Kim Clijsters beat Flavia Pennetta 6-0 6-1 to reach the semi-finals of the Rogers Cup in Toronto.
The seventh-seeded Belgian needed just 40 minutes to set up a meeting with Russia's Anastasia Myskina who defeated Argentina's Gisela Dulko 6-4 7-5.
Defending champion Amelie Mauresmo went through when her opponent Nadia Petrova retired with a muscle injury with the Frenchwoman leading 4-6 7-5 2-0.
She will face fourth seed Justine Henin-Hardenne in the last four.
The Belgian had to battle hard to get past Czech player Nicole Vaidisova 7-5 7-6.
Myskina v Clijsters
Henin-Hardenne v Mauresmo
Petrova called for a trainer after losing the first game of the third set to Mauresmo and received treatment on the injury.
She played one more game before informing the chair umpire she could no longer continue.
"I think I was able to step up and really play better and better as the match was going," said Mauresmo.
"I didn't think I was playing bad. But she was very solid, didn't give me any free points, and I was going for things and missed a few shots here and there that made the difference.
"In these kinds of matches, it's just two or three points that can make the difference in one set."
Myskina achieved her victory despite a sprained ankle sustained during her win over Shinobu Asagoe on Thursday and had to undergo intensive physiotherapy to face Dulko.
"Some moves it really bothers me, but some of them were ok," said Myskina after the win.
"I didn't really think that Gisela played really smart with me, so that was a big advantage for me. The drop shot was the key but she didn't use it."