It wasn't the right-hander's finest outing, as he threw 82 pitches in his first four frames and needed to finagle out of a couple of jams.
But Zimmermann has found a way to get through seven innings, needing just 30 pitches in his final three frames and retiring eight of the last nine Giants hitters he faced.
He leaves with the Nats holding a 6-1 lead after seven, and after notching a victory in just one of his last six starts, Zimmermann is in line for his 14th win of the season.
Zimmermann's final line: 7 IP, 6 H, 1 R, 2 BB, 2 Ks, 112 pitches, 75 strikes
The right-hander had pitched to a 6.75 ERA in four starts since the All-Star break, but he brings those numbers back down a bit with today's outing.
Ian Krol comes on to work the eighth for the Nats, who are now six defensive outs from pushing their winning streak to five, which would match their season high.
Update: The fact that Davey Johnson will need to use Tyler Clippard and Rafael Soriano for a second straight day when the Nats held a five-run lead going to the eighth is yet another indication of how shaky the Nationals' middle relief has been lately.
Krol surrendered a solo homer to Brandon Belt with one out in the eighth - a ball that was absolutely crushed - and then Ryan Mattheus allowed two more runs himself on a Pablo Sandoval double to right-center, making it a 6-4 game.
Johnson needed to call on Clippard to get the final two outs of the inning with Sandoval in scoring position and the tying run at the plate, and yet again, Clippard delivered, striking out Roger Kieschnick and Gregor Blanco swinging to get out of the jam.
Clippard's ERA drops to 2.06 after another stellar outing, but the Nats are relying on the goggled right-hander far too much lately. Drew Storen is in the minors, Mattheus is struggling mightily, Krol and Fernando Abad have dropped off and Craig Stammen has been somewhat shaky.
For now, order has been restored, and the Nats will take at least a two-run lead to the ninth, where Soriano will try and close this out. But the bullpen has to be a concern for Johnson right now.
Update II: Soriano owes Denard Span a nice steak dinner and an expensive bottle of wine.
Span laid out to make a game-saving diving grab on a Hunter Pence line drive to the gap with two outs in the ninth inning, preserving a 6-5 Nationals win and sending the 30,657 at Nats Park home happy.
What a tremendous play, and in a huge spot.
This marks the Nats' fifth straight win, tying for their longest winning streak of the year.
This five-game stretch puts the Nats at 59-60 on the season, with a chance to get back to .500 before a three-game set in Atlanta starting Friday.