Diaz had his second consecutive three-hit game to lift the Braves to their fourth consecutive win and drop the Phillies into a tie with Florida for first in the NL East.
With the score tied at 2, Brian McCann led off the eighth with a single off Ryan Madson (2-4). Pinch-runner Jair Jurrjens moved to second on Yunel Escobar's sacrifice. Diaz followed with his run-scoring double to the center-field wall.
Pinch-hitter Garret Anderson added his first career pinch-hit homer, a two-run shot off Madson.