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.
Nadal, a three-time champion in Canada, took 71 minutes to beat 20-year-old Croat Coric, facing just one break point in the match.
The Spaniard meets Denis Shapovalov next - the Canadian who was disqualified from his Davis Cup match against Great Britain in February for hitting the umpire in the face with the ball.
Another Canadian, sixth seed Milos Raonic, who could have played Nadal in the last eight, lost 6-4 6-4 to unseeded Frenchman Adrian Mannarino.
Gael Monfils saved four match points before beating Japanese fifth seed Kei Nishikori 6-7 (4-7) 7-5 7-6 (8-6), while Germany's fourth seed Alexander Zverev saved three match points as he overcame Richard Gasquet 6-3 4-6 7-6 (7-3).
In the last 16, Zverev will face Australia's Nick Kyrgios, who brushed aside Victor Troicki 6-1 6-2.