The defending World Series champion Nationals have lost seven consecutive games. The NL East-leading Braves have won five in a row.
Nationals fielder Juan Soto was scratched less than an hour before the game because of a sore left elbow and also did not start the second game. Another outfielder, Adam Eaton, also was held out after leaving Thursday night's game at Philadelphia with a jammed knee.
Acuna slammed his bat to the ground in apparent frustration after hitting what appeared to be a harmless flyball in the first inning. Nationals center fielder Victor Robles kept drifting back as the ball kept carrying before finally clearing the wall in center field.
Nationals right-hander Austin Voth was as surprised as Acuna to see the ball clear the wall.
''I thought he hit it pretty well, high,'' Voth said. ''I didn't think it had the distance. I was kind of shocked when it went out.''
Acuna walked to open the third before Swanson's homer to left-center off Voth (0-5), who allowed five runs and seven hits, including three homers, in 4 2/3 innings.
In the fourth, Acuna lined his seventh homer, also to center field, to drive in Adam Duvall, who doubled.
Acuna was on the injured list from Aug. 12-25 with left wrist inflammation and this week was held out with a sore hamstring.
''He kind of picked up where he left off and that's good for us,'' Braves manager Brian Snitker said.
Swanson drove in three runs. His single in the sixth drove in Tyler Flowers, and Adeiny Hechavarria scored when Michael A. Taylor misplayed the ball in right field for an error.
Acuna and Swanson continued the Braves' big power week. Marcell Ozuna and Duvall became the first teammates in the majors to have three-homer games in consecutive games on Tuesday and Wednesday at Boston.
Tommy Milone gave up one run on six hits with no walks in four innings. He made his second start since he was acquired by the Braves from Baltimore. Darren O'Day (3-0) pitched a scoreless fifth.
Nationals: Manager Dave Martinez said he hoped Eaton avoided a serious injury when he left Thursday night's game with a jammed knee. ... 3B Carter Kieboom, who was hitting .200 with no homers when he was sent to the team's optional training site on Aug. 26, joined the Nationals in Atlanta. Martinez said he wanted to ''watch his swing and see where he's at.''
Braves: 2B Ozzie Albies (bone contusion in right wrist) took batting practice. He was placed on the IL on Aug. 5. ... LHP Cole Hamels (triceps tendinitis) is expected to throw batting practice on Sunday as he tries to move closer to his 2020 debut.
Asdrubal Cabrera hit a triple off the right-field wall in the fourth. Cabrera scored when Duvall, celebrating his 32nd birthday, made a leaping catch over the left-field wall to take a homer from Yan Gomes.
Nationals: RHP Erick Fedde (1-3 4.71 ERA) will face the Braves for the first time this season, and the first time in Atlanta, on Saturday night.
Braves: LHP Max Fried (6-0, 1.60) will try to remain undefeated after allowing only eight runs in his first eight starts.
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