"It's nice to have both of them going at the same time," Washington manager Jim Riggleman said of Zimmerman and Dunn, who now have a combined 58 homers on the season. "That's probably about as far as I've seen [Zimmerman] hit a ball."
Jason Marquis earned his first win of the season, allowing three runs on seven hits, three walks and a hit batsman in 5 2/3 innings of work.
"It was a grind," Marquis said. "I put myself in trouble a couple times, but my defense picked me up."
Marquis (1-7) pitched out of a two-out, bases-loaded jam in the third, inducing a 2-1 flyout by Gaby Sanchez. Emilio Bonifacio singled, and Logan Morrison and Hanley Ramirez drew walks to load the bases for Sanchez.
The Marlins threatened again in the fourth and the fifth, and each time Marquis escaped without allowing any runs. Rookie Mike Stanton was hit by a pitch, and Cameron Maybin's bunt single put runners on first and second in the fourth. But Marquis got catcher Brett Hayes to hit into a double play.
In the fifth, Bonifacio hit a one-out single and stole second, and Morrison walked, but Ramirez and Sanchez flied out.
Marquis's two-out luck ran out in the sixth, as Hayes hit a two-run homer to left field to cut the Nationals' lead to 4-3. Joel Peralta relieved Marquis after the blast and struck out pinch-hitter Donnie Murphy to end the inning.
Washington added four insurance runs in the seventh. Justin Maxwell reached on an error and scored following two wild pitches. After two outs, Bernadina walked and stole his 13th base and Zimmerman walked. Dunn worked the count full before depositing the payoff pitch over the center-field wall.
Ramirez hit a two-out solo home run in the first to put the Marlins up 1-0. Dunn tied the game in the top of the second with an RBI double that also scored Zimmerman. Zimmerman reached base on a single up the middle that sloshed its way to Maybin, who kicked up puddles as he ran to field it.
The Marlins threatened again in the second. Chad Tracy led off with a single, but Zimmerman executed his signature 5-4-3 double play on the fleet-footed Maybin.
The Nationals got seven hits off Sanabia, who exited after 5 2/3 innings.
Both starting pitchers had to stay fresh. Heavy rain showers persisted from 6 p.m. ET until about 9 p.m. and then the game, originally scheduled to start at 7:10 p.m., began at 9:59 p.m.
Several Washington players voiced concern about the wet field.
"I was thinking [about] how much water was gonna be in my shoes," right fielder Michael Morse said. "I've never seen a field like that. We were lucky not too many balls were hit out there."
Zimmerman was thankful for the timely hitting in the watery conditions.
"We want to [get those hits] every single time," Zimmerman said. "We have a good offense. We have young guys, and it will go up and down."