Britain's Katie Boulter was eliminated while Venus Williams and Julia Goerges progressed on a rain-hit first day at the Rogers Cup in Montreal.
Boulter suffered a straight-sets defeat to Lesia Tsurenko in 85 minutes, the Ukrainian winning the first-round tie 6-4 6-2.
The 22-year-old from Leicestershire had been targeting a victory that would probably have taken her in to the top 100 of the women's world rankings.
British number one Johanna Konta, meanwhile, and her Chinese partner Shuai Zhang were involved in an epic doubles match at the last-32 stage.
The pair recovered to beat Romanian duo Irina-Camelia Begu and Simona Halep 4-6 7-6 (7/1) 11-9 in a game lasting one hour and 45 minutes.
In other action, number 10 seed Julia Goerges came back from the brink to win in her match with Timea Babos.
The German lost the first set and the second went to a tie, but she fought on to win 3-6 7-6(7 /3) 6-4.
Goerges will play Lucie Safarova in the second round after she beat Daria Gavrilova.
Number 13 seed Williams saw off Caroline Dolehide 7-5 6-1, although her fellow American - who is 110 places below her in the WTA ranking - served well with three aces.
Serena Williams, who pulled out on the eve of the competition, revealed on Monday she had been dealing with the emotional strain of balancing motherhood with her search for further glory.
Back on court, Anastasija Sevastova beat Aleksandra Krunic to set up a second-round clash with number seven seed Garbine Muguruza and Anett Kontaveit defeated Ekaterina Makarova to meet number eight seed Petra Kvitova.
Magdalena Rybarikova beat Barbora Stycova to book a match with Caroline Garcia, the sixth seed.