Nick Kyrgios was dismissed by Stan Wawrinka, Novak Djokovic saw off a spirited challenge by lucky loser Mirza Basic and Grigor Dimitrov scraped by on day two of the Rogers Cup.
Rain interrupted proceedings again in Toronto, forcing number five seed Dimitrov's fragmented second-round tie with Fernando Verdasco to go on late into the night.
Wild card Wawrinka came back from a set down and slugged it out with Kyrgios over two hours to beat the number 16 seed 1-6 7-5 7-5 in the first round.
Kyrgios's relatively light work of Wawrinka in the opening set saw him break the former world number three twice.
But the Australian, who pulled out of the Citi Open with a hip injury, struggled to keep up the pace with Wawrinka, himself on a comeback after knee surgeries.
His first singles outing since winning Wimbledon, Djokovic met Basic for a first-round tie.
The four-time tournament champion and former world number one served nine aces to beat the lucky loser 6-3 7-6 (7/3).
Dimitrov squeaked past Verdasco after their rain-blighted match was decided by a tiebreak.
The world number five was buzzed by the number 31 in the opening game, losing serve.
He took Verdasco to two break points himself but lost the set 6-4.
Dimitrov came back in the second, breaking his opponent twice to win 6-2 before rain stopped play with the score 4-4 in the third.
It was gone 11pm by the time play resumed and Verdasco, almost winning a match point in the 10th game, took the game to a tiebreak, which the Bulgarian won 7-6 (7/5).
In other games, Marton Fucsovics set up a second-round clash with Wawrinka by beating Joao Sousa 6-4 7-6 (7/2).
Sam Querry beat Adrian Mannarino 6-2 7-5 and will meet number 11 seed Diego Schwartzman, who knocked Kyle Edmund out in the first round.
Wild card Vasek Pospisil lost to Borna Coric 6-4 6-3 and the Croatian will play number six seed Marin Cilic in the second round.
A second-round tie with number three seed Juan Martin del Potro awaits Robin Hasse after the Dutchman beat Kei Nishikori 7-5 6-1.
And Kevin Anderson, the number four seed, will play qualifier Evgeny Donskoy in the second round following the Russian's defeat of countryman Andrey Rublev.