Top seed and defending champion Rafa Nadal overcame a slow start to beat British qualifier Dan Evans 7-6, 6-4 while Stefanos Tsitsipas and John Isner both fell in second-round upsets at the Rogers Cup in Montreal on Wednesday.
Nadal, playing his first match since losing to Roger Federer in the Wimbledon semi-finals, fell behind 5-2 in the tiebreak before roaring back to prevail in his first career meeting with world No 53 Evans.
The Spaniard jumped to a 2-0 lead in the second set before the players were forced off court for a rain delay and when play resumed Evans got back on serve at 3-3 before Nadal regained his confidence and proved too strong.
The French Open champion said he did not make an ideal start as he struggled to adjust to a new playing surface given the amount of time he logged on clay and grass in recent months.
"After Wimbledon always the mind goes down a little bit because I have been playing long claycourt season, then grass, so you didn't relax," Nadal told reporters.
"Then when you finish Wimbledon, it's like your body lose a little bit that tension, so it needs little bit of time to recover.
"Today, as I said before, the main thing is win. I know with victories that other things should be coming slowly."
Up next for Nadal, a four-times champion in Canada who has never successfully defended a hardcourt title in his career, will be Argentine Guido Pella, who was a 6-3 2-6 7-6(2) winner over Moldova's Radu Albot.
Hubert Hurkacz defeated world number five Tsitsipas 6-4 3-6 6-3 for the Pole's fourth win over a top 10 opponent this year.
The crucial moment came with Tsitsipas facing a break point and trailing 4-3 in the third set.
Hurkacz hit a passing shot that got past the charging Tsitsipas but the Greek believed the shot was wide.
Tsitsipas was angry that he could not challenge the call since there was no Hawkeye review system available to the players on the outside court.
"It's a joke! It's a Masters 1000 event!" Tsitsipas yelled at the chair umpire.
Isner failed to convert any of his break point opportunities and his usually deadly serve didn't quite fire as he fell 6-3 6-4 to Cristian Garin of Chile.
Garin will face Daniil Medvedev, who crushed Kyle Edmund 6-3, 6-0 in their second-round match earlier in the day.
An all-Canadian battle between Felix Auger-Aliassime and Milos Raonic ended with a whimper when the big-serving Raonic was forced to retire from the match with an apparent back issue ahead of the third set.
In other second-round action, Frenchman Richard Gasquet upset Japanese fifth seed Kei Nishikori 6-7, 6-2, 7-6 and Croatian 14th seed Marin Cilic was a 6-3 6-4 winner over Australian lucky loser John Millman.
Second seeded Dominic Thiem, sixth seeded Karen Khachanov and Frenchman Gael Monfils all advanced to the round of 16 on Wednesday.
Italian seventh seed Fabio Fognini capped the evening session with a 7-6, 6-3 win over American qualifier Tommy Paul.