Novak Djokovic did not let a late switch in opponent throw him off his stride in his quest for a fifth Rogers Cup title as he subdued Bosnian lucky loser Mirza Basic 6-3, 7-6(3) in first-round action on Tuesday.
Djokovic, the ninth seed, was originally scheduled to play Australian Open semi-finalist Chung Hyeon but the 22-year-old South Korean withdrew with a back injury about an hour before the match was due to start.
The Serb, competing in singles for the first time since his Wimbledon triumph last month, was never in real danger during the first-round clash, but he still needed some time to figure out Basic before wrapping up the match in 90 minutes.
"I've never played Basic. I've known him, I've practiced with him, but I've never played an official match so definitely not easy to find a rhythm from the beginning of the match," said Djokovic.
"There were frustrations at times but that means I care."
The Serbian World No 10 was not as sharp as he will need to be if he hopes to triumph here for the first time since 2016, but it was enough on a day when Basic was misfiring on both his forehand and serve.
Djokovic broke Basic in the sixth game of the first set to go ahead 4-2 and then wrapped up the opener three games later when he fired an ace down the middle.
The former world number one was up a break in the second set and cruising along until Basic broke back in the eighth game to draw level 4-4, leaving Djokovic yelling at himself in frustration while swatting a ball out of the court.
Basic did well to hold serve and pull ahead, but the more experienced Djokovic kept calm and booked his place in the second round, where he will face Canadian Peter Polansky.
In other first-round action, Swiss wild card Stan Wawrinka upset 16th-seeded Australian Nick Kyrgios 1-6, 7-5, 7-5 while Dutchman Robin Haase beat Japan's Kei Nishikori 7-5, 6-1.
Hometown favourite Bouchard falls in Montreal
The vocal support of the home crowd was not enough to carry Canadian Eugenie Bouchard into the second round of the Rogers Cup in Montreal on Tuesday as she fell 6-2, 6-4 to Belgian Elise Mertens.
Mertens, the 14th seed, won five break points to dispatch Bouchard, who has fallen to 129th in the world after reaching a career-high of fifth in 2014 -- the year she reached the Wimbledon final.
Home hopes now rest on 21-year-old Francoise Abanda, who defeated qualifier Kirsten Flipkens of Belgium 6-3, 6-2.
British No 1 Johanna Konta fired eight aces en route to a 6-7(6), 6-1, 6-2 upset win over 11th-seeded Latvian Jelena Ostapenko.
Konta, who handed Serena Williams the worst loss of her career at the Silicon Valley Classic last month, will face former world number one Victoria Azarenka in the second round on Wednesday.
Azarenka was in complete control as she strolled to a 6-0, 6-1 win over Kristina Mladenovic of France in a match that lasted less than an hour.
Daria Kasatkina, seeded 12th, beat rising Greek talent Maria Sakkari 6-4, 4-6, 6-1 to set up her first career meeting against fellow Russian Maria Sharapova in the second round on Wednesday.
Other players to advance from the first round on Tuesday included Spaniard Carla Suarez Navarro and Russian Anastasia Pavlyuchenkova, who will face top-seeded Simona Halep on Wednesday.
Sixth seed Caroline Garcia of France and eighth-seeded Czech Petra Kvitova advanced to the third round with wins over Slovak Magdalena Rybarikova and Estonian Anett Kontaveit.