The left-hander was 0-8 with a 6.33 ERA in nine previous starts away from AT&T Park, but he allowed no runs on four hits over seven-plus innings to earn his first road victory of the season.
Houston's hitters were baffled all night, getting just two hits through the first five innings and striking out eight times.
"I didn't see many pitches; all his stuff was great," Astros right fielder Hunter Pence said. "I was getting jammed. [Sanchez] had some incredible stuff and it was some of the best stuff I've seen from a left-hander."
Sanchez's night on the mound was made even better when he snapped a 40-at-bat hitless drought with a single in the fifth. Over the last five starts dating back to his no-hitter on July 10, he is 3-1 with a 2.75 ERA.
"Lately I've been throwing less pitches per inning and getting deeper into the game," Sanchez said. "That's what's expected from me and that's what I'm trying to do."
With Sanchez cruising on the mound, the Giants' bats came to life.
San Francisco caught a break when Roy Oswalt, who was originally supposed to start the game for Houston, had his start pushed back with a nagging back injury. In his place, the Astros sent Felipe Paulino to the mound, and the Giants took full advantage, jumping on the right-hander for runs in each of the first three innings.
"That kid has great stuff and is going to be a good pitcher," Bochy said. "We've seen him twice and he's a good young pitcher. Every at-bat was a quality at-bat. We had good at-bats, and after a tough night [Monday] and against him we just got good pitches to hit."
After being unable to drive home the tying run with two outs in the ninth inning Monday, Bengie Molina quickly put the previous night behind him and came through in his first at-bat, doubling into the left-center-field gap to score Sandoval from first base to give the Giants an early 1-0 lead.
Eugenio Velez extended the Giants' lead and his career-long hit streak to 11 games by lacing an RBI single through the right side of the infield in the second, scoring Winn. Rowand kept the hit parade going in the third and the fifth to extend the Giants' lead to 5-0.
With the bases loaded in the third, Rowand singled to drive in two more runs off Paulino. He then closed the book on the Astros starter by doubling off reliever Doug Brocail in the fifth to drive in Winn, who had walked and was the last batter Paulino faced in his 4 1/3 innings.
"[Paulino] had problems putting hitters away," Astros manager Cecil Cooper said. "His stuff was good, his velocity was good, but he just didn't make enough quality pitches."
If the five-run lead wasn't enough for Sanchez, the Giants clubbed back-to-back home runs in the sixth. Freddy Sanchez and Sandoval became the second pair of Giants to hit back-to-back home runs this season, pushing the lead to 7-0 with consecutive solo home runs.
Sandoval was taken out of the game with tightness in his right side after his 17th home run of the season and was seen talking to trainers in the dugout before coming out in favor of Jaun Uribe. He is expected to be back in the lineup Wednesday.
"They got good pitches to hit, both Sanchez and Sandoval and they took advantage," Bochy said. "[Sandoval] just got a little tight on the right side and with where the game was, with the score, we wanted to give him a break."