Bouchard, who was seeded No. 6, won less than half her service points, had five double-faults and was broken five times.
The Westmount, Que., native, a Wimbledon finalist last year, has a 6-4 record this year. Her career record at Key Biscayne fell to 1-3.
Maria, a German ranked 113th, beat a top 10 player for the first time since 2010.
In the opening stadium match, No. 4 Caroline Wozniacki rallied to beat Kaia Kanepi 4-6, 6-1, 6-3. In men's play, No. 4 Kei Nishikori defeated Mikhail Youzhny 6-2, 6-1.