With the score tied 4-4, Ian Desmond led off the sixth with a double off Kris Medlen (1-1) and scored the go-ahead run one out later when Tracy, batting for Tyler Moore, sliced a 1-0 pitch into the left-center field gap.
Danny Espinoza belted a three-run homer for National League East-leading Washington, which logged its fifth win in six games.
Strasburg surrendered four runs on six hits over five frames, allowing four walks while striking out six.
Dan Uggla socked a two-run homer for the third-place Braves, who fell three games behind the Nationals in the NL East.
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