Cincinnati completed a 6-1 homestand, having opened it with a four-game sweep of St. Louis.
Dunn had been relatively quiet on the homestand and had just six hits in his last 33 at bats entering Sunday's game. But he ended it with a bang, launching a solo homer in the third inning and a three-run shot in the fifth to help stake the Reds to a 7-0 lead. Dunn also had an RBI single in the first inning.
The home runs were the 11th and 12th of the season for the lefthanded slugger, tying Dunn with Milwaukee's Richie Sexson for the league lead.
The Brewers nearly erased the deficit, but left the bases loaded in the ninth. After a bloop RBI single by Eddie Perez pulled the Brewers within 7-5 in the ninth, pinch-hitter Royce Clayton lined out to first. Alex Sanchez, who was seven for 11 with the bases loaded in his career, then grounded out to short to end the game.
Reds starter Jeff Austin (2-1) pitched five scoreless innings before yielding a two-run, inside-the-park homer to Eric Young in the sixth and solo shots to Geoff Jenkins and Perez in the seventh.
Scott Williamson picked up his ninth save in as many chances despite giving up a run in the ninth.
Milwaukee starter Wayne Franklin (1-4) was knocked out in the fifth after surrendering seven runs and six hits.