Rodriguez (11-6) allowed five hits and struck out three in his first start since leaving his outing eight days ago with a strained right hamstring. The left-hander won his sixth straight decision and gave up one earned run or fewer for the seventh consecutive appearance.
"I felt strong today," Rodriguez said. "Eight days and no pitching. My arm feels strong."
In the last two weeks, Rodriguez, Roy Oswalt and Mike Hampton have all been injured. Oswalt will start Tuesday in Florida after leaving his last start with a sore back and Hampton left Saturday's game after two innings with a lateral meniscus tear in his right knee.
Houston manager Cecil Cooper was unsure how long Rodriguez would last after missing a full week, but Rodriguez seemed to pitch better with each inning.
"Wandy was terrific, maybe not as strong as he'd been in the past, but I still thought he was up to the challenge and he got better as the game wore on," Cooper said.
Jose Valverde got the final four outs for Houston to earn his 15th save of the season and second of the series.
The Brewers were shut out for the fourth time in games Gallardo has started. The 23-year-old right-hander lost two 1-0 decisions before Sunday.
"I've been losing a lot of close games," Gallardo said. "Hopefully, I'll get it turned around. I just think I threw very well. The only pitch they put a good swing on, it beats me."
Rodriguez had shaky command early, walking leadoff man Felipe Lopez on four pitches. In the second, Rodriguez hit Jason Kendall with a pitch and walked Gallardo, but escaped a two-out, bases-loaded jam when Lopez grounded out.
"I missed a lot on my location because I didn't see any hitters for eight days," Rodriguez said.
Gallardo allowed three hits in the first three innings, including a double by Jason Michaels. Michaels, who homered twice in Friday's 6-3 Astros win, came in batting .345 in his last 19 games.
Lee walked with one out in the fourth before Blum launched a 1-0 pitch into the right-field seats, his seventh homer of the season.
Rodriguez allowed only four hits after the second inning. Bill Hall singled with one out in the sixth before J.J. Hardy to rolled into a double play. Lopez singled with two outs in the seventh and Mike Cameron flew out on Rodriguez's 116th pitch.
"We expected Wandy to pitch well, but I don't think any of us expected him to go that deep into the game," Blum said. "For two runs to hold up against a lineup like the Milwaukee Brewers' [lineup], that's pretty good."
Jeff Fulchino relieved for the eighth and Michael Bourn helped him with an over-the-shoulder, running catch on Casey McGehee's fly ball to deep center. The Brewers put two men on with two outs before Valverde relieved and retired Craig Counsell on a popup.
The Astros have won seven of the last nine games Rodriguez has started.
Milwaukee manager Ken Macha said right-handers Dave Bush and Jeff Suppan may start rehab assignments this week. Bush (3-4, 5.67 ERA) is nursing a triceps tear and Suppan (5-8, 5.27 ERA) is recovering from an oblique strain. ... Oswalt threw about 40 pitches in the bullpen, his last tuneup before Tuesday's start. ... Milwaukee acquired right-handed reliever David Weathers from Cincinnati for a player to be named later. Weathers is 3-3 with a 3.32 ERA in 43 games.