Petra Kvitova and Samantha Stosur eased through their openers at the Rogers Cup on Monday.
Kvitova, the 2012 champion in Montreal, and Stosur, runner-up a year earlier, were untroubled at the WTA Premier event.
Stosur got the better of Heather Watson in straight sets, while Kvitova dropped just three games against Magda Linette.
Elina Svitolina, the only other seed in action, also advanced on a rainy day. KVITOVA, STOSUR PROGRESS
The 12th-seeded Kvitova needed less than an hour to dispose of Linette 6-1 6-2 in Canada.
The Czech managed to break serve four times and did not face a break point.
Stosur faced more of a test but still managed to get past Brit Watson 7-5 6-3 in the first round. GOOD DAY FOR SEEDS
It was an excellent day for seeds, with Svitolina joining Kvitova and Stosur in the second round.
The Ukrainian 17th seed was a 6-2 6-4 winner over American qualifier Jennifer Brady. LUCIC-BARONI DOMINATES, BRENGLE RALLIES
Croatian veteran Mirjana Lucic-Baroni lost just nine second-set points in a 6-2 6-0 thrashing of Nao Hibino.
Madison Brengle came from behind to beat Ekaterina Makarova, recovering from 4-2 down in the third set to claim a 6-4 1-6 6-4 win. MUGURUZA, HALEP BEGIN CAMPAIGNS
French Open champion and third seed Garbine Muguruza starts her campaign against qualifier Naomi Broady. Simona Halep, the fifth seed, faces a potentially tricky clash against Australian Daria Gavrilova.