Gallardo (6-6) handcuffed the Reds on three hits and a walk, and struck out five. He stretched his scoreless innings streak to 14 as the Brewers posted their first shutout win of the season.
Francisco belted a two-run homer in the fifth inning for a 4-0 Milwaukee lead after earlier driving in a run with a sacrifice fly.
Logan Schafer went 3-for-4 with two RBI and two runs scored for the Brewers, who evened their three-game series.
Cincinnati's Homer Bailey (4-5) was saddled with the loss after surrendering six runs on eight hits in seven frames.