The Braves faced a 9-0 deficit through five innings, but came back to take a one-run lead in the top of the ninth. Washington then tied it in the bottom half of the inning on Danny Espinosa's homer, but Tom Gorzelanny (2-2), the Nationals' sixth pitcher, surrendered the winning run in the 11th.
Uggla reached on an infield single to open the inning, went to second on a throwing error by third baseman Ryan Zimmerman and took third on a passed ball. Uggla then raced home on Janish's base hit.
Atlanta scored four runs in both the sixth and eighth innings and still trailed by one heading into the ninth. The Braves took a brief lead in the ninth on a two-run triple by Michael Bourn.
Washington's lead over Atlanta at the top of the National League East was reduced to 2 1/2 games.
Notable deaths of 2014 [PHOTOS]
Michael Sam cut from the Dallas Cowboys