Murray and Zverev among host of stars to advance in Toronto
Murray worked through a marathon opening set before dominating the second for a 7-6 (7/3), 6-0 victory over Italy's Lorenzo Sonego.
The 36-year-old Scotsman, with three Canadian titles on his resume, earned his first victory in the country since his 2015 trophy as he defeated the Italian in two hours, eight minutes in a challenging wind.
Germany's Zverev, who defeated Roger Federer for the 2017 Canadian title, reached the second round by defeating Dutchman Tallon Griekspoor 6-4, 7-6 (7/3).
Third seed Casper Ruud began his US Open run-up after a bye, struggling at the start but wrapping up a 7-6 (8/6), 6-4 defeat of Jiri Lehecka for a 199th career ATP match win.
The Norwegian trailed 4-0 in the first-set tiebreaker but found form in his first hardcourt match of the summer to reach the third round.
"I told myself not to give up, just keep holding onto the score," he said. "I saved a couple of set points.
"It was all about luck and margins and they were on my side. By the end of the second set I was hitting and serving better - I'm happy how I progressed in the match."
Murray won his only previous encounter with Sonego last February in Doha, saving three match points. Murray, ranked 40th to his opponent's 39th, also lifted the trophy here in 2009 and 2010.
Murray's opening set lasted 90 minutes, with the two-time Wimbledon winner saving set points in the 10th game.
He profitted from Sonego's 44 unforced errors to sweep into the second round.
"I'm really pleased to have won. Those were blustery conditions," Murray said. "The wind was changing conditions during the points.
"We knew it would be like this after hitting here this morning. The breeze added a bit of stress."
Murray said getting through the first set was a challenge.
"It was tight, there were a lot of opportunities on both sides," he said. "I managed to sneak through the tiebreaker, he probably got disappointed and I relaxed a bit in the second set.
"I hope to build confidence and win a few matches," said the three-time Grand Slam champion, who exited last week in the Washington third round to Taylor Fritz.
"I had success here but it was a long time ago. Hopefully I can build some momentum."
Former ATP number two Zverev, seeded 13th and playing here for the first time in four years, extended his current win streak to six matches after taking his home event in Hamburg last month.
The German battled the wind for an hour and three-quarters to prevail.
He sent down an ace for three match points and won as his opponent missed on a drop shot attempt.
Evans and Norrie ousted
Zverev ended with 27 winners and 20 unforced errors - the exact reversal of Griekspoor's 20 and 27.
"It was a win in tough conditions," Zverev said. "It was very windy.
"I'm just happy to get through. I hope it gets nicer to play tomorrow."
Britain failed to get two men into the second round as 11th-seeded Cameron Norrie went down 7-5, 6-4 to weekend Los Cabos finalist Alex de Minaur of Australia.
Britain suffered another blow as Dan Evans, who took his first ATP title in 2 1/2 years on Sunday at Washington, lost to Canadian wild card Gabriel Diallo 7-6 (7/4), 7-5, the local taking his first tour-level match triumph.
Canada lost its number one as Felix Auger-Aliassime suffered his fifth consecutive loss on his 23rd birthday, falling 6-4, 6-4 to Australian qualifier Max Purcell, the world number 78 whose next foe will be Murray.
