The Marlins swept a three game series and handed the Nationals their seventh consecutive loss.
Hendrickson (2-1) allowed a run on three hits, helping Florida to its fifth win in six games. The loss went to Odalis Perez (0-2), who gave up two runs on six hits in 5 2/3.
Josh Willingham doubled home a run in the ninth to put the Marlins in front by two and then saved the game with a defensive play in the bottom half of the inning.
With a runner on second base and one out, Washington's Nick Johnson drove a ball deep to left. Willingham jumped high to prevent the ball from going over the fence and swatted it back in play.
Instead of being a two-run homer, it turned out to be a one-run double.
Kevin Gregg then worked his way out of trouble to earn his second save.