Third seed Mona Barthel crashed out of the Coupe Banque Nationale in Quebec after losing her first-round match against Latvian Jelena Ostapenko on Monday.
The German world number 48 was expected to overcome an opponent some 53 places below her in the WTA world rankings but slumped to a 7-6 (8-6) 4-6 6-4 defeat despite serving 12 aces.
Briton Naomi Broady is through to the second round, however, thanks to a 6-3 7-6 (9/7) victory over Alla Kudryavtseva of Russia.
Bulgaria's Sesil Karatantcheva joins her in the next round after she beat Czech Barbora Krejcikova 6-3 7-5, while Krejcikova's compatriot Andrea Hlavackova was a 7-6 (10/8) 6-0 victor over American Shelby Rogers.
Earlier in the day Rogers' compatriot Louisa Chirico defeated qualifier Julia Boserup 7-5 4-6 6-1.