The Braves snapped a four-game skid and avoided a three-game sweep at the hands of the Nationals, who own the best record in baseball. Washington leads Atlanta by six games at the top of the National League East.
Medlen (5-1) has worked mostly as a reliever in his three-year career, but he has established a unique record as a starter for the Braves. Atlanta has won the last 16 games he has started dating to May 2010 -- the longest such streak in team history.
Atlanta had a 2-1 lead heading into the ninth, but scored three times in the inning against Tom Gorzelanny.
Martin Prado broke a scoreless tie in the fifth with a two-run double.
The loss went to Ross Detwiler (7-6), who allowed two runs on seven hits in 5 1/3 innings.