Canada opened up a scoreless game with four runs in the top of the eighth.
Joey Lye's single scored a pair of runs and was followed by Jennifer Salling's sac fly and Erika Polidori's RBI single.
The Americans scored a pair of runs in the bottom of the eighth, but could not complete the comeback.
The loss was the first of the tournament for the U.S., which had cruised through the tournament with a perfect 5-0 record including two wins over Canada.
The Canadian men won gold earlier at the Games with a 2-1 win over Venezuela.
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