Britain's Anne Keothavong lost her opening match at the inaugural WTA Brazil Cup.
Keothavong, the world number 183, went down in straight sets against seventh seed Kristina Mladenovic, who is 125 places higher in the rankings.
Mladenovic, from France, prevailed 6-3 6-4 and will play Germany's Tatjana Malek in the second round of the hardcourt event in Florianopolis.
Top seed Venus Williams eased past Croat Mirjana Lucic-Baroni 6-3 6-3 in her first-round assignment, while fifth seed Magdalena Rybarikova saw off Japanese vetern Kimiko Date-Krumm 6-3 6-0.
But third seed Kirsten Flipkens made an early exit, the Belgian losing 2-6 6-4 6-4 to Russia's Olga Puchkova.