Bengie Molina fought out of an 0-2 hole, singling to score Jose Castillo, and Aurilia hit a 1-2 pitch after Ray Durham had drawn a four-pitch walk to load the bases. Bowker then came up against reliever Luis Ayala and got his fifth homer of the season and first career grand slam.
"Richie's at-bat was really an unbelievable at-bat," Bowker said. "(It) kind of fired me up. To go up there and do that, it was awesome."
Sanchez (5-3) allowed four singles, walked two and struck out four in seven innings. Aurilia finished with three hits for San Francisco, which relied on a big inning for the second straight night to again subdue the Nationals.
"He is so focused out there and he is maintaining it no matter what is happening," Giants manager Bruce Bochy said of Sanchez. "Men on base, he's not losing that. That was his biggest problem early as starter. You have to have that for the time you are out there."
Tyler Walker and Pat Misch each got three outs to finish off the four-hitter, San Francisco's fifth shutout of the season. The Giants have won 10 of 16 games and five straight on the road.
Washington was blanked for the ninth time this year and third time in seven games. The Nationals have dropped six of seven overall, scoring only three runs in those six defeats.
"Everybody knows we're struggling offensively, but Sanchez is a good pitcher," Nationals manager Manny Acta said. "Obviously, when you're struggling offensively against a good pitcher, you run into nights like this."
The Giants, who had a seven-run third inning in a 10-1 victory over Washington on Friday, sent 10 men to the plate in the eighth.
Bowker said his approach was simple.
"Just trying to be more patient at the plate," Bowker said. "That's the key to hitting I think -- swinging at the good pitches and laying off the bad ones."
Shawn Hill, winless in 11 starts dating to Sept. 10, retired 15 straight batters after a second-inning single by Omar Vizquel. But Hill (0-3) got no offensive support from his teammates, who matched a season high by hitting into three double plays.
"When you get ahead, you make the hitters swing early and you get ground balls. Like today, I got three double plays and that got me out of jams," Sanchez said. "They are a team that is aggressive. They swing at first pitch a lot in the late innings. After the fifth inning, they were swinging at the first pitch, so I was using my sinker and my changeup."
Hill gave up two runs and seven hits in 7 1/3 innings. He struck out two and walked one in his longest outing since going eight innings April 30.
"The first couple of innings, it seemed like they were jumping all over the early pitches -- the fastballs -- just trying to get ahead," Hill said. "As soon as I started to mix in some of the offspeed pitches, it kind of kept them honest."
After the game, the Nationals released OF Rob Mackowiak, who was hitting .132 with a home run and four RBIs in 38 games. Washington is expected to recall RHP Garrett Mock to start Sunday's game, which would be his major league debut. ... Nationals C Jesus Flores extended his hitting streak to a career-best nine games with a seventh-inning single. ... Sanchez has gone at least six innings and allowed two or fewer earned runs in each of his last five starts. ... Bowker's homer was his first since May 12, a span of 60 at-bats.