Yovani Gallardo is unbeaten as a starter when he homers.
Gallardo (6-2) gave up two runs in seven innings with four strikeouts. He hit a solo homer in the seventh inning -- the sixth of his career -- to help halt the Brewers three-game skid.
"He's tough, that's their ace," Marlins manager Fredi Gonzalez said. "It's tough to score runs."
All six of his home runs have came in Brewers victories.
"He should hit more homers," Brewers manager Ken Macha said.
Brewers slugger Prince Fielder also hit his ninth home run of the season and the second in two days.
"I really wanted to finish that sixth inning, but I left a fastball over the plate to Gomez, but overall I felt good about this performance," Volstad said.
Gallardo, batting eighth in the lineup, led off the seventh with a home run off lefty Taylor Tankersley.
"He's kind of known for being a pretty good hitting pitcher," Volstad said. "His average wasn't super high, but around the league people know he can swing it a little bit."
With two outs in the top of the eighth inning and the score tied, Gomez stepped to the plate against Jorge Sosa (1-1) with Casey McGehee on second. Gomez gave the Brewers the lead hitting a line drive to left-center field on the first pitch by Sosa for the 3-2 edge.
George Kottaras immediately followed and hit a deep home run to right field despite breaking his bat on the blast for a 5-2 advantage.
"It felt good off the bat, I felt the bat explode," Kottaras said. "I looked up and the ball's carrying and it went out."
Dan Uggla scored on a groundout by Ronny Paulino in the bottom of the inning to pull the Marlins within two, but Fielder hit a solo homer and Craig Counsell hit an RBI single in the ninth to push lead to 7-3.
John Axford pitched 1 2-3 innings to earn his third save despite allowing an RBI double to Hanley Ramirez.
Jorge Cantu hit a sacrifice fly and and an RBI single to give the Marlins the early lead.
"I got out of some jams where I had to make some good pitches and just keep it there at 2-0 and give my team a chance to go up there and swing the bats," Gallardo said.