The Reds optioned Petty to Triple-A Louisville on Saturday.
Petty gave up three runs (two earned) in 1.2 innings while serving as the Reds' opening pitcher in Friday's 5-3 loss to the Nationals, and he'll now head back to the minors to open up a spot on the active roster for righty Ron Marinaccio, who was claimed off waivers from Pittsburgh. Petty now owns a 4.83 ERA and 1.26 WHIP through 31.2 innings this season.