Ryan Braun hit an early two-run double and Khris Davis added a three-run homer in the eighth, his third shot in three games.
Cruz leads the majors with 19 home runs. He has three homers in two days, and 12 in May.
He’s never had such a prolific month in the majors.
“Maybe in the minors, but not in the big leagues,” Cruz said. “I think the approach I’ve been taking the last few weeks has been pretty good.”
Braun hit a hard chopper down the first-base line for his two-out double with runners on second and third. Milwaukee scored four times in the eighth off relievers Brad Brach and Brian Matusz after Baltimore had drawn within 4-3.
That inning was capped by Davis’ high fly that sailed past the left-field pole for his ninth homer of the season.
The NL Central-leading Brewers took two of three in the first interleague series between the teams since 2008.
On Tuesday night, Gallardo delivered a game-winning RBI double as a pinch-hitter in the 10th inning. He went 1 for 2 on Wednesday, though the rest of the lineup took care of the offense.
“To add on late like that - huge,” manager Ron Roenicke said. “We keep waiting for one of those and we got it.”
On the mound, Gallardo (3-3) gave up three runs on four hits and five walks in 6 2-3 innings. He also went 1 for 2 at the plate.