The Blainville, Que., native lost 6-3, 7-5 to Caroline Garcia of France at the Masters tournament in Miami.
Wozniak was looking to follow up momentum in her comeback from injuries after wins in last week's Indian Wells tournament over top players Urszula Radwanska, Sabine Lisicki and Anastasia Pavlyuchenkova.
For her part, Garcia also owns wins this year over Canadians Eugenie Bouchard and Sharon Fichman.
Fichman of Toronto faces Coco Vandeweghe of the United States later Tuesday in a qualifying match.
Montreal's Françoise Abanda, who just turned 17 last month, will play a qualifier against the oldest player on the women's tour, 43-year-old Kimiko Date Krumm of of Japan.
Peter Polansky of Toronto is in action in the main draw on the men's side against Dominic Thiem of Austria.
Bouchard of Westmount, Que., Milos Raonic of Thornhill, and Vancouver's Vasek Pospisil received byes into the second round of the tournament.