Defending Rogers Cup champion Jo-Wilfried Tsonga enjoyed a first-up win, as did world number one Novak Djokovic.
Novak Djokovic started his US swing with a two-set victory at the Rogers Cup, while defending champion Jo-Wilfried Tsonga enjoyed progression past the first round.
Top-ranked Djokovic proved too good for Thomaz Bellucci, advancing 6-3 7-6 (7-4) off just the one break of the world number 33's serve in Montreal.
Djokovic will face either Jack Sock or Grigor Dimitrov in the third round of the ATP 1000 hard-court event.
Tenth seed Tsonga, playing at his lowest ranking since 2008, was a 6-4 6-4 winner over Borna Coric.
Tsonga's ranking slipped to 24th on Monday, just the second time he has been outside the top-20 in seven years - but the Frenchman started well as he defends a Masters-level title for just the second time.
His match with Coric had been held over due to rain on Monday - Tsonga resumed at 2-1 up in the first set - a fate that halted Andy Murray on Tuesday.
Second seed Murray, looking to bounce back from his shock loss to Teymuraz Gabashvili first-up at the Citi Open in Washington, took on Tommy Robredo - but the poor weather in Canada stopped the match with the Scot serving at 4-4 40-30.
Eighth seed Milos Raonic was the biggest name to fall, Ivo Karlovic taking him down 7-6 (7-1) 7-6 (7-1) in a historic match.
Karlovic surpassed 10,000 career aces in the seventh game of the second set, just the second player to do so after fellow Croatian Goran Ivanisevic.
Earlier in the set, Karlovic also chalked up his third 1,000-ace season in his career - making it back-to-back years he has reached four figures.
Kevin Anderson, seeded 12th, was the only other seed to exit the event, with Lukas Rosol edging the South African 7-6 (7-2) 7-6 (7-4).
Vasek Pospisil provided the only joy among the Canadian contingent, the wildcard a 6-4 6-3 victor over qualifier Lu Yen-hsun.
Pospisil reigned despite failures from Raonic, and veteran wildcard Frank Dancevic - who lost 6-2 6-4 to Spain's Pablo Andujar.
Andujar's countryman Roberto Bautista Agut defeated Janko Tipsarevic 6-3 6-4, while Tipsarevic's fellow Serbian Viktor Troicki joined him in making an early exit - losing to Russian qualifier Mikhail Youzhny 6-3 7-5.
Qualifier Ernests Gulbis saved two match points in his 3-6 7-6 (10-8) 6-1 triumph over Dominic Thiem.
Sock and 16th seed John Isner flew the American flag high.
Isner got past Benjamin Becker 6-4 6-7 (6-8) 6-3, while Sock edged out Adrian Mannarino 6-2 2-6 7-6 (7-5).
Steve Johnson, who reached the semi-finals in Washington last week, was comfortably humbled by 13th seed David Goffin 6-2 6-2.
Bulgarian 14th seed Dimitrov saw off qualifier Alexandr Dolgopolov 6-4 7-5.
Jeremy Chardy eased past lucky loser and fellow Frenchman Nicolas Mahut 6-1 7-5, and Nick Kyrgios' first match since losing in the Wimbledon fourth round saw him dispatch of Fernando Verdasco 6-3 4-6 6-4.