The Nationals took two out of three in the series in the first segment of a nine-game road trip. Washington won a battle of the bull pens after neither starter made it past the sixth inning.
Colorado held a 3-2 lead heading into the seventh, but Washington's Ian Desmond scored the tying run in that inning on a balk and the Nationals struck for two more in the eighth.
Roger Bernadina and Zimmerman came through with back-to-back, one-out doubles to account for the tiebreaking run and Zimmerman scored later in the inning on a single by Desmond.
That second run became vital when Todd Helton's two-out, RBI single in the ninth brought the Rockies within one. Rafael Soriano picked up his 17th save when he got Jonathan Herrera on a line drive to shortstop that ended the game.
Craig Stammen (4-2) earned the victory with two innings of one-hit relief. Matt Belisle (4-3) gave up both of Washington's eighth-inning runs to take the loss.