Zimmerman (2-3), who logged his first win since April 25, mostly baffled the Reds for seven innings. The right-hander scattered five hits and a walk and struck out nine, allowing just one Cincinnati runner to reach home.
Tyler Clippard tossed a scoreless eighth and Henry Rodriguez struck out the side in the ninth for his eighth save as the Nats improved to 21-12 and maintained their half-game lead over Atlanta atop the National League East.
Danny Espinoza and Wilson Ramos each cracked solo homers to account for Washington's offense.
Jose Arredondo (2-1) was saddled with the loss after allowing Ramos' tie-breaking shot in the sixth.
Brandon Phillips got the only RBI for Cincinnati, which fell for the third time in four games.
Putin thinks Obama would save him if he were drowning
Rosie O'Donnell unveils nearly 50-pound weight loss