MIAMI -- Mike MacDougal's first pitch produced an inning-ending double play. His last pitch did the same.
"We probably don't want to make them that exciting, but we'll take it," MacDougal said.
Pinch-hitter Mike Morse broke a tie in the sixth inning with a two-out, two-run double for the Nationals, who had lost their six previous games at Florida this year. Adam Dunn and Ryan Zimmerman homered for Washington.
MacDougal got the final five outs, completing a five-hitter for his 15th save in 16 chances. The Marlins, clinging to slim playoff chances, have lost only two of their past nine games -- both to last-place Washington.
"All night we had some people on base with the right guys at the plate," Florida manager Fredi Gonzalez said. "They made some pitches."
The Marlins went 0 for 8 with runners in scoring position -- and 0 for 3 against MacDougal in those situations.
Washington led 5-2 in the eighth when MacDougal came on with runners at the corners and one out. He needed only one pitch to end the inning on John Baker's grounder to second.
"I'm sure hoping for a double play if there's a guy on first," MacDougal said. "I'm pitching to one. It doesn't always work, but if there's a guy at first base, I'm trying to get them to hit a ground ball."
Dan Uggla hit his 28th homer for the Marlins to start the ninth. Cody Ross followed with a single and Ross Gload walked, but MacDougal struck out Emilio Bonifacio and retired Chris Coghlan on another double-play grounder.
Dunn hit a two-run homer in the first inning, his 37th. Zimmerman's 29th homer came in the seventh.
NL batting leader Hanley Ramirez walked three times after hitting a first-inning two-run homer, his 23rd. Those were the only runs off J.D. Martin (4-4), who went five innings.
Florida ace Josh Johnson failed in a bid for his 15th win, pitching only five innings for the second game in a row and departing for a pinch-hitter with the score 2-all. The Marlins want to avoid overworking the right-hander, who has pitched a career-high 188 1/3 innings after returning from reconstructive elbow surgery in July 2008.
"We've got to keep an eye on it," Gonzalez said. "It's a concern."
Johnson struck out eight, walked four, allowed two hits and threw 89 pitches. He said his arm felt fine, and he wanted to stay in the game.
"I understand where they're coming from, but at the same I time I want to be out there," Johnson said. "That's the competitor I am. There's nothing you can do about it. There's nothing I can say that's going to change their mind."
Brian Sanches (4-2) relieved Johnson and walked Josh Willingham to start the sixth. Will Nieves singled with two out, and Morse drove in both runners.
Morse, who grew up in South Florida, had a cluster of family and friends in the skimpy crowd of about 4,000.
"I'll say 4,200, because a lot of people came just to see me," he said with a grin.
Willie Harris led off the game with a walk, and Dunn's homer gave Washington a brief 2-0 lead. Dunn is batting .345 against Florida this year with five homers.
Nick Johnson walked and Ramirez homered in the bottom of the first to tie the game.
Florida's Andrew Miller pitched one inning in his first appearance since July 17 and gave up Zimmerman's homer.
RHP Chris Volstad will rejoin the Florida rotation and start Sunday. In his past two starts, he has allowed 10 earned runs in 5 2/3 innings. ... Nationals SS Ian Desmond spent the night on the bench after hitting a homer and driving in four runs in his major-league debut Thursday. Manager Jim Riggleman said Desmond may see playing time at 2B and in the OF before the season ends. ... SS Ramirez has gone a career-best 55 consecutive games without an error.