Joey Votto cracked a grand slam in the third inning and the Reds went on to beat the Tigers 9-5 at Great American Ball Park.
Cincinnati built a 9-0 lead before Detroit made it look closer than it was with five runs in the top of the ninth.
Sal Romano improved to 4-and-7, tossing seven shutout innings with six strikeouts in the opener of the two-game series.
Matthew Boyd was charged with the loss after giving up five runs on six hits, including a grand slam, while striking out five and walking three in four innings.
Reliever Drew VerHagen left the game in the seventh after he suffered a broken nose when he was hit in the face with a throw while covering first base.
In this afternoon's series finale, Michael Fulmer goes to the mound for the Tigers, while the Reds counter with Tyler Mahle.