Maldonado's sixth-inning blast -- his second of the series -- boosted the Brewers to their fourth win in five games overall.
Ryan Braun went 2-for-3 with a two-run shot and an RBI single, backing seven strong innings from Yovani Gallardo (5-5), who yielded just one earned run five hits over seven full frames.
Padres starter Anthony Bass (2-6) lasted 5 2/3 innings, during which he surrendered four runs on five hits.
Will Venable went 3-for-5 with a solo homer and three hits for San Diego, which fell to a major league-worst 6-21 on the road.
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