Fielder hits No. 40 to help Gallardo win his 13th
Fielder, who came in tied with Albert Pujols with a majors-best 127 RBIs, hit a solo shot in the first and then set a club record in the fifth when he walked for the 100th time this season.
He set a franchise record when he recorded his 127th RBI with a sacrifice fly in the Brewers' win Saturday.
Corey Hart and Jody Gerut also homered for Milwaukee.
Gallardo (13-12) became the fourth Milwaukee pitcher with 200 strikeouts in a season and first since Ben Sheets' 264 in 2004 when Astro starter Felipe Paulino was caught looking in the third.
Gallardo gave up a single and two doubles, struck out seven and walked three. It was the first sweep by Milwaukee of Houston since a three-game set last season from May 30-June 1.
The 23-year-old right-hander, who was on a pitch count, threw 77 pitches and left after the fifth with Milwaukee ahead 4-0. The team is shutting him down after 185 2-3 innings in his first full year of action. He missed most of last season with separate knee injuries.
Carlos Villanueva, Chris Smith and Mike Burns pitched scoreless relief to preserve the victory for Gallardo and help Milwaukee extend their winning streak to five games, their longest since a season high seven-game run from May 12-19.
The Astros lost their the seventh consecutive game and matched the longest losing streak of the season set on May 21-27.
Felipe Paulino (2-10) extended his career-worst losing streak to six games. He gave up four runs and eight hits in six innings. Paulino walked two and struck out seven. He hasn't won since beating Detroit on June 27. The right-hander also failed to get any run support for his fourth consecutive start.
Milwaukee gave Gallardo a 3-0 lead in the first when Hart hit a two-run homer, his 12th, and one out later, Fielder drove a 3-2 pitch to dead center. Hart's last home run was July 27, but this was the first since being reinstated from the disabled list Sept. 8 after undergoing an emergency appendectomy on Aug. 2.
Gerut connected off Paulino in the fourth for his eighth homer of the season and fourth since being acquired from San Diego on May 21 for Tony Gwynn.
Gerut, who went 3-for-4, added a run-scoring double in the eighth.
Craig Counsell drew a walk off Tim Byrdak with the bases loaded in the eighth to force in the sixth run.
Notes: Manager Ken Macha and the entire Brewers team presented a trophy to Prince Fielder in a pregame ceremony at homeplate. Astros manager Cecil Cooper, who set the record in 1983, came out to shake hands with Fielder. ... Carlos Lee's second-inning double extended his hitting streak to a season-high 12 games. ... The Astros lost for the 18th time in the team's last 23 games at Miller Park. ... Doug Davis and Teddy Higuera, who did it twice, also passed the 200 strikeout plateau for Milwaukee.