All of the Atlanta runs scored on long balls, allowing the Braves to bounce back from a setback on Wednesday against Kansas City that ended a 10-game winning streak.
The game was still tied at 4-4, however, when Gattis came through with a one-out blast in the eighth that delivered Andrelton Simmons in front of him.
Anthony Varvaro (1-0) picked up the win with two innings of relief. Craig Kimbrel struck out the side in the ninth for his seventh save.
The homer by Gattis came off Jared Hughes (1-1), who worked 1 1/3 innings.
Notable deaths of 2014 [PHOTOS]
Julius Randle breaks leg during NBA debut