France's Marion Bartoli and Russia's Svetlana Kuznetsova suffered shock first-round exits from the Rogers Cup as the two seeded players were eliminated on Monday by a pair of gritty qualifiers.
World number nine Bartoli fell 6-3, 6-3 to Kazakhstan's Galina Voskoboeva while world number 15 Kuznetsova followed her out of the $2 million tournament when she was upset 4-6, 6-4, 6-3 by Romania's Simona Halep.
"When you commit so many mistakes like I did today, it's really hard to win a match," Bartoli, the tournament's ninth seed, said.
"It was really like my game was not at the level I'm supposed to play regarding my ranking. That was the main problem."
Two-times Grand Slam winner Kuznetsova seemed in control as she took the first set against Halep but had no answer for the Romanian qualifier, who ended the match winning over 70 percent of her first serve points.
Tenth-seeded Samantha Stosur of Australia overcame a slow start to get past Japan's Ayumi Morita 4-6, 6-2, 6-3 and will face the winner of Tuesday's match between Aleksandra Wozniak of Canada and Shahar Peer of Israel.
Kuznetsova gains revenge for loss to Schiavone
Wozniacki regains world number one ranking
Nadal, Wozniacki top seeds at Australian Open
Sharapova advances in Auckland, Kuznetsova out
Stosur beaten by Dulko in third round