Cueto (19-9) yielded a pair of runs on five hits, didn't allow a walk and struck out five, becoming the first right-handed Reds pitcher since Jack Billingham in 1974 to reach the 19-win plateau.
Jonathan Broxton tossed a scoreless eighth and Aroldis Chapman picked up his 36th save for the National League Central champion Reds.
Mike Fiers (9-9) surrendered four runs on nine hits over 4 1/3 innings for Milwaukee, which fell 4 1/2 games behind the St. Louis Cardinals for a National League wild card spot.
Aramis Ramirez homered for the Brewers.
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