The Cardinals opened their longest road trip of the season, 11 days, 10 games, with their fourth loss in five games.
Reds star Joey Votto doubled and singled, driving in a run and scoring one, a day after his tantrum at home plate following an ejection.
Jaime Garcia (8-5) lasted a season-low 4 1-3 innings and gave up six runs. He had been 5-0 in seven starts since losing to the Reds on July 28.
John Lamb (1-3), one of three left-handers acquired from Kansas City for Johnny Cueto in late July, shook off control problems for his first major league win. He walked six, struck out six and gave up three hits in five innings.