Canada's Rebecca Marino lost 6-3, 6-7 (5), 4-6 to China's Zheng Qinwen in the opening round of the National Bank Open on Tuesday.
The Vancouver native entered the tournament coming off a quarterfinal appearance at the Citi Open, where she fell to Daria Saville of Australia.
Marino, who made it into the WTA top 100 rankings for the first time since 2012 and is currently No. 96, got rolling early as she took the first set with relative ease.
Marino overcame a strong start from Zheng in the second set, but had trouble with unforced errors in the tiebreaker.
The Canadian went up 4-3 in the final set before losing the final three games.
Marino fired 12 aces to Zheng's 10 and was a perfect 2 for 2 on break points in the loss.
The 19-year-old Zheng, ranked 51st, will next play fifth-ranked Ons Jabeur in the second round.