Rafael Nadal and Roger Federer both won their opening matches at the Rogers Cup in Montreal.
Top seed Nadal, 31, who will claim the world number one spot from Andy Murray if he reaches the semi-finals in Canada, beat Borna Coric 6-1 6-2.
Murray pulled out of the competition with a hip injury, which has also ruled him out of the Cincinnati Masters.
Federer, playing in his first match since winning the Wimbledon title, beat Peter Polansky 6-2 6-1 in 53 minutes.
The 36-year-old's 32nd victory of the season sets up a third-round meeting with Spain's David Ferrer, who upset 15th seed Jack Sock 7-6 (9-7) 3-6 6-1.