Medlen struck out 13 Nationals batters over seven innings, recording 19 swings and misses in the process.
Atlanta broke open the scoring in the bottom of the fourth against Ross Detwiler. A leadoff double by Freddie Freeman and a walk to Dan Uggla put runners on first and second with no one out. David Ross followed with a grounder that got Uggla on a force out at second, but that was all. With runners on first and third, Andrelton Simmons hit a sacrifice fly to right field that plated Freeman and gave the Braves a 1-0 lead.
The only mistake Medlen made came in the top of the sixth inning as Bryce Harper launched his 19th home run of the season to left field to tie things at one.
Medlen left after seven, allowing just the one run and five hits.
Eric O' Flaherty pitched a scoreless eighth, and Craig Kimbrel struck out the side in the top of the ninth to eventually earn the win.
In the bottom of the ninth, back-to-back singles from Andrelton Simmons and Michael Bourn put runners on first and third against Sean Burnett. Tyler Pastornicky followed with a grounder to short that Ian Desmond fired wide to home plate, making Simmons safe at the plate and giving the Braves a 2-1 win.