Former Red Jose Guillen popped two home runs and Ryan Zimmerman and Matt LeCroy each added one before Alfonso Soriano capped the display in the ninth with a 492-foot blast that cleared the center-field batter's eye.
"Just another night at the ballpark," said manager Frank Robinson, who participated in some impressive displays of Queen City power during his first 10 seasons in the Majors with the Reds. "It's the ballpark. They were good swings. Any time you hit the ball out of the ballpark, it's a pretty good swing. Some swings are better than others. Soriano's would've been out of the Grand Canyon."
Right-hander Tony Armas went three batters into the seventh inning while improving to 3-2. All three wins have come in his last three road starts.
"It doesn't matter where they come, as long as they come -- for me and the team," Armas said.
"He was lights out until the seventh," Robinson said. "He was throwing nice and easy. He located his pitches in the zone and kept the hitters off balance."
Joey Eischen and Gary Majewski teamed up to get out of a bases-loaded, nobody-out jam in the seventh while allowing just one run. Left-hander Mike Stanton and right-hander Jon Rauch each pitched a scoreless relief inning.
The Nationals went into the game hitting .227 as a team at home and .266 on the road.
"I don't know what it is," Robinson said. "We haven't been at home very much. We have to go home sooner or later, in July and August, and I just hope we play better.
"I've seen clubs like this. I've been on clubs like this. They're more relaxed and at ease. Things are flowing on the road."
Every starter except first baseman Nick Johnson got at least one hit, including Armas. Royce Clayton went 3-for-4 with two doubles, while LeCroy, Marlon Byrd and Jose Vidro each had two hits.
Byrd, who went into the game hitting .050 at home and .348 on the road, singled in each of his first two at-bats. He was stranded in the first, but he followed Clayton's leadoff double and Armas' sacrifice bunt with a broken-bat, bloop single to left to give Washington a 1-0 lead in the third.
Zimmerman followed in the fourth with his fifth home run of the season and first since April 30 at St. Louis. He has hit four of his five home runs on the road this season.
Armas got into the act with a single to center in the fourth for his first hit in 10 at-bats this season, but Clayton was thrown out at the plate by Ryan Freel to end the inning.
Guillen made it 3-0 with his fourth homer of the season and second in two games on Brandon Claussen's first pitch of the sixth inning. One out later, LeCroy added his first homer of the season.
Guillen has hit four of his five home runs away from Washington.
"This is a nice ballpark to come and play in," Guillen said. "Sometimes, it's nice to get away from home. RFK is not a fun place to play."
Soriano's ninth-inning blast is the fourth-longest on record at Great American Ball Park and fifth to clear the center-field batter's eye. It was his 10th of the season and inflated the lead to 7-1.