Posey is now 19-for-37 (.514) during this trip. He's got six homers, 13 RBIs and 11 runs scored during the 10-game stretch.
"He's had quite a road trip," Giants manager Bruce Bochy said after Saturday's victory. "He'll be back there tomorrow. His catching, throwing, his bat -- he's really impressed everybody."
This performance raised his average to .351 over 37 games. He's already gotten seven homers and 23 RBIs but said afterward that he's more excited that the Giants (46-41) have won six of 10 games on this trip.
"I try not to have too many expectations," Posey said. "I just try to go out and play as hard as I can and have the results take care of themselves. I'm excited about winning."
His defense also helped the winning. Washington (39-49) was trying to add to a 5-4 lead in the bottom of the sixth when Posey almost singlehandedly stopped the Nationals. Mike Morse led off the inning with a double, and Ian Desmond then bunted to try to move pinch-runner Roger Bernadina to third.
But Posey quickly pounced on the bunt and threw out Bernadina.
"I felt like it was barely out in front of the plate," Posey said. "It was a good opportunity to kill the inning."
Desmond stole second moments later before Posey gunned him down going for third. The Giants then turned the game around by scoring four runs in the top of the seventh off Tyler Clippard (8-6) for an 8-5 lead.
Bochy said Aaron Rowand's one-out, game-tying solo homer sparked the team in the seventh. Clippard then walked Freddy Sanchez and Aubrey Huff before Posey gave San Francisco the lead for good with an RBI single. Juan Uribe then ended his recent 0-for-23 drought with a two-run double off Doug Slaten for an 8-5 lead.
Posey then made it 10-5 with a two-run homer in the ninth off Miguel Batista. A fan caught the shot at the right-field railing, but it was upheld after video review.
Giants starter Jonathan Sanchez got an early two-run single but struggled on the first anniversary of his no-hitter. He gave up five runs on five hits in 3 2/3 innings, but the San Francisco bullpen saved the day.
Joe Martinez, Santiago Casilla (2-2), Chris Ray, Sergio Romo and Jeremy Affeldt combined to hold Washington to no runs on three hits in the final 5 1/3 innings. They also set down the final 10 Nationals as the Giants rallied from a pair of early two-run deficits.
"Martinez saved us [and] Casilla got out of a tough [jam]," Bochy said. "Ray, Romo and Jeremy all threw the ball great. That's what it takes to win a game like that, to have the bullpen holding them at bay, and you give the club a chance to come back."
Martinez has been a starter throughout his Minor League career. But he's split time between the bullpen and starting when he's been with the Giants.
Martinez was just recalled Friday, and Bochy said he'll likely spend most of his time as the long man. That's what Martinez did in this game, giving up three hits and no runs in 1 2/3 innings and setting the table for the rest of the bullpen to do their jobs.
"It's a little different; it feels a little different," said Martinez. "But I guess I got the job done as close to well as possible [and] kept us in it."
That let Posey take charge. He got a double, single and homer in his last three at-bats over the final four innings. The rookie has to cool off at some point.
But the Giants are hoping it's not any time soon.