Gallardo (2-1) labored for a third straight start despite getting plenty of run support over his six innings. After allowing two runs in his first two starts, he's given up 15 in his past 16 1-3 innings.
Both manager Brad Mills and pitching coach Brad Arnsberg were ejected in the second inning as the Astros fell to 0-13 when allowing four or more runs.
Braun's shot in the third inning landed in the Brewers' bullpen in left field to put Milwaukee up for good 4-2 and sparked a curtain call. Braun's extension will keep him in Milwaukee through 2020, and he got a standing ovation in his first at-bat before he did his damage in his second plate appearance.
The deal guarantees Braun at least $145.5 million, and the investment seems as if it's a wise one right now.
Braun is off to the best start of his career and has reached base safely in all 19 games, the longest streak by a Brewer to start a season since Paul Molitor equaled that mark in 1991. After his 3-for-4 performance against the Astros, Braun is hitting .382 so far this year.
Fans held up lots of signs in support of Braun's big decision.
One read, "Go treat yourself to something nice" and another had a picture of a beer and a bratwurst with a greater than sign opposite a beach scene.
Gallardo's homer made it 5-3 in the fourth and Yuniesky Betancourt drove in two runs to give Milwaukee a 7-4 lead in the fifth with a hard single underneath the glove of Astros third baseman Matt Downs that was first called an error.
Casey McGehee's double with the bases loaded and two outs in the sixth off reliever Jose Valdez scored two and Mark Kotsay followed with a two-run single that made it 11-4. Gomez's three-run shot off Enerio Del Rosario made it 14-6.
Jonathan Lucroy's run-scoring fielder's choice gave Milwaukee a 1-0 lead in the second just after home plate umpire Paul Schrieber ejected Arnsberg and crew chief Joe West booted Mills from the game following a mound visit.
The Astros went ahead 2-1 on Michael Bourn's run-scoring single and Angel Sanchez's sacrifice fly in the third before Braun erased it.
Houston cut it to 4-3 on Humberto Quintero's single in the fourth and 5-4 on Hunter Pence's fielder's choice in the fifth, but couldn't match Milwaukee's potent offense despite scoring twice more in the seventh and once in the eighth.
NOTES: Brewers 2B Rickie Weeks (left pinkie sprain) left in the sixth inning. He slid headfirst on a stolen base earlier in the inning. ... Brewers OF Brandon Boggs was called up Friday to replace OF Nyjer Morgan (thigh bruise). Morgan went on the 15-day DL on Thursday, retroactive to April 18. ... Astros 2B Clint Barmes (broken left hand) will take infield practice on Saturday, then leave for a rehab assignment at Triple-A Oklahoma City. ... Astros 2B Bill Hall, who played for the Brewers from 2002-09, made his first appearance back at Miller Park.