Defending champion Annika Beck is out of the Coupe Banque Nationale after Barbora Stefkova saved two match points to beat the second seed.
Beck claimed her last WTA title singles title in Quebec City last year, but there will be no repeat this week after Stefkova stunned the world number 38 with a 2-6 7-5 6-3 victory.
Lucky loser Stefkova fended off two match points in the second set, winning four games in a row, before breaking three times in the final set to book a place in the second round.
The 176th-ranked Czech served seven aces and sealed a shock win despite being broken on seven occasions in a topsy-turvy encounter.
Fourth seed Julia Goerges also fell at the first hurdle, going down 6-4 7-6 (7-1) to Russian Ekaterina Alexandrova.
Oceane Dodin finally celebrated her first WTA Tour match win of the year by ousting fifth seed Naomi Broady 2-6 6-4 6-4.
It was a day of upsets, completed when sixth seed Mona Barthel was beaten by Canadian wildcard Francoise Abanda 7-6 (9-7) 6-4.
Sachia Vickery needed almost three hours to overcome Patricia Maria Tig 7-6 (7-5) 6-7 (3-7) 7-6 (9-7).
Alison Van Uytvanck eased past Elitsa Kostova 6-1 6-2 and qualifier Tereza Martincova won an all-Czech battle against Barbora Krejcikova 4-6 7-5 6-4.