Harris drove in five runs and reached base five times, Jesus Flores had four hits and Austin Kearns hit a two-run homer as the Nationals routed the Braves 15-6 on Sunday.
Washington outscored Atlanta 23-8 to win the last two games of the series. The series loss was a crushing disappointment for the fourth-place Braves, who hoped for a strong start after the All-Star break.
The only highlights for Atlanta were two homers by Mark Teixeira, who had three hits and drove in three runs, and a two-run homer by Martin Prado in the fourth off Odalis Perez (3-7).
The Braves didn't play as if capable of making a second-half move in the NL East. They matched their season high with four errors and issued eight walks while.
Washington set season highs for runs and hits (17) to cap a successful start to its nine-game road trip.
The Nationals rocked Jo-Jo Reyes (3-9) for seven hits and six runs in 2 1-3 innings and then added six runs in 1 2-3 innings against Buddy Carlyle.
Reyes suffered his fifth straight loss.
Washington put the game away early, scoring 12 runs while loading the bases in the second, third and fourth innings. The Nationals loaded the bases again in the ninth against Royce Ring, when Felipe Lopez, who had three hits, drove in his third run with a sacrifice fly.
Perez pitched five innings, giving up nine hits and five runs, in his first win since May 28.
Harris had two hits, including a two-run homer, and three walks. He had a two-run single in the second, a bases-loaded walk in the third and a two-run homer in the fourth. Kearns added his two-run homer in the fourth.
Harris had seven hits, seven RBIs and scored five runs in the series. He finished one RBI shy of his career-high six set with the Braves on July 21, 2007, when he had six hits against St. Louis. The Cairo, Ga., native hit .270 in 117 games, including 78 starts, for Atlanta last season but was not re-signed.
Flores drove in two runs with his career-high four hits.
The Braves' frustrations were evident in the third inning, when Carlyle's bases-loaded walk to Harris forced in a run for a 6-1 lead.
Carlyle pulled his jersey over his mouth in an apparent attempt to hide his complaints about home plate umpire Chris Guccione's tight strike zone. Guccione immediately stepped in front of the plate to warn Carlyle, and then he turned to caution Braves manager Bobby Cox not to come out of the dugout.
Cox still bounced up the dugout steps and was quickly ejected by Guccione. Cox continued to follow Guccione for a long tirade before finally returning to the dugout. Cox continued to yell from the dugout before the umpire again stepped away from home plate and pointed the way for Cox to leave.
Notes: The ejection was the 141st of Cox's career and his sixth of the season. ... Prado's homer was his first of the season and the first of his career as a pinch-hitter. ... The Nationals, who placed 1B Dmitri Young on the 15-day disabled list after Saturday night's game, also have Aaron Boone on the disabled list. Paul Lo Duca, primarily a catcher, started at first base in each game of the series, and manager Manny Acta said infielder Ronnie Belliard, who started at third base, is the top backup at first.