Uggla, who was released by the Braves last year, singled to right-center field in the second inning and then trotted home when Tyler Moore followed with a two-run home run off Alex Wood.
After the Nationals increased their lead to 3-0 with the help of three consecutive one-out hits off Jason Grilli, the Braves produced a game-tying, three-run third inning against Taylor Jordan, who surrendered a solo homer to Pedro Ciriaco and then allowed both Freeman and Jonny Gomes to notch consecutive two-out RBI singles.
After the Nationals used three walks and Moore's three-run triple to construct a four-run fourth against Juan Jaime, the Braves tallied four runs of their own during the bottom half of the inning against Craig Stammen.
Freeman started the barrage by sending a two-run shot over the right-center field wall and Ciriaco added to Stammen's woes with a two-out, two-run double.
The Nationals erased a one-run deficit with a pair of seventh-inning runs surrendered by Arodys Vizcaino. Matt Skole started the rally with a leadoff double and Kila Ka'aihue capped it with a go-ahead sacrifice fly.
Up Next: The Braves will play their first split-squad games that begin on Saturday at 1:05 p.m. ET. Shelby Miller will make his Braves debut in the home game against the Tigers. Top pitching prospect Mike Foltynewicz begins his battle for the rotation's fifth spot when he starts against the Mets in Port St. Lucie, Fla.
Mark Bowman is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.