Rafael Soriano pitched the ninth for his 39th save in 45 chances.
Wilson Ramos and Ian Desmond each had three hits and drove in two runs for the Nationals. Ryan Zimmerman and Ramos homered and Denard Span extended his hitting streak to 19 games, the longest active streak in the majors.
Justin Ruggiano had three of the Marlins' six hits and Jacob Turner (3-6) allowed five runs in four innings.
REDS 3, DODGERS 2
CINCINNATI (AP) — Ryan Hanigan's RBI double in the ninth inning drove in Zack Cozart from first base to lift Cincinnati past Los Angeles.
Cozart, who had extended his career-high hitting streak to 13 games earlier, started the rally with a one-out single to left off Ronald Belisario (5-7). Hanigan lined the next pitch past left fielder Carl Crawford to the wall, and Cozart beat shortstop Hanley Ramirez's relay throw with a headfirst slide.
Aroldis Chapman (4-5) pitched a perfect ninth with two strikeouts to get the win, which completed the Reds' first sweep of a three-game series against the Dodgers in Cincinnati since June 12-14, 1992.
Jay Bruce hit two home runs for the Reds, who went into the game in third place in the NL Central, two games behind first-place St. Louis, which beat second-place Pittsburgh earlier Sunday.