World number one Novak Djokovic booked his place in the last 16 of the Rogers Cup although Andy Murray was thwarted by bad weather in Montreal.
Djokovic was rarely troubled despite having to come through a second set tie-break as he began his campaign for a fourth title with a 6-3 7-6 (7/4) victory over Brazil's Thomaz Bellucci.
"Credit to him for playing some really solid, resilient tennis, not giving up, getting a lot of balls back, serving well," said Djokovic, playing in his first match since winning Wimbledon last month, on the ATP Tour website.
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"He's an all-round player, I think he's improved over the years."
Second seed Andy Murray's last-32 match with Tommy Robredo came to an early conclusion because of the inclement weather, with play abandoned at 4-4 and 40-30 on the Scot's serve.
There was a shock defeat for Milos Raonic, the home hope and eighth seed losing 7-6 (7/1) 7-6 (7/1) to fellow big server Ivo Karlovic.
Defending champion Jo-Wilfried Tsonga kicked off his tournament with a first-round 6-4 6-4 victory over Borna Coric, while there were also wins for seeded trio David Goffin, Grigor Dimitrov and John Isner.
Goffin, seeded 13th, thrashed Steve Johnson 6-2 6-2, 14th seed Dimitrov eased out Alexandr Dolgopolov 6-4 7-5 and Isner, the 16th seed, came through 6-4 6-7 (6/8) 6-3 against Benjamin Becker.
There were also wins for Lukas Rosol, Pablo Andujar, Roberto Bautista Agut, Jeremy Chardy, Ernests Gulbis, Nick Kyrgios, Vasek Pospisil, Jack Sock and Mikhail Youzhny.
In the women's draw in Toronto, top seed Serena Williams hit back from a set down to beat Flavia Pennetta 2-6 6-3 6-0 in the second round.
Britain's Heather Watson crushed fellow qualifier Irina Falconi 6-1 6-2 in her opening-round match but there was another early exit for Eugenie Bouchard, with the Montreal-native defeated 6-0 5-7 6-2 by Belinda Bencic.
Ninth seed Carla Suarez Navarro was edged out 6-3 6-7 (2/7) 6-4 by Alize Cornet, while 10th seed Karolina Pliskova and Timea Bacsinszky, seeded 12th, were beaten by Mirjana Lucic-Baroni and Alison Riske respectively.
Victoria Azarenka, Julia Goerges, Dominika Cibulkova, Carina Witthoeft, Madison Brengle, Sara Errani, Olga Govortsova, Polona Hercog, Ekaterina Makarova, Lesia Tsurenko, Angelique Kerber, Barbora Strycova, Jelena Jankovic, Monica Puig, Roberta Vinci, Daria Gavrilova and Andrea Petkovic all progressed into the second round.