Mahle made his Major League debut Sunday, a mixed bag of pitching results during a 5-2 Reds' loss to Pittsburgh at Great American Ball Park.
The 22-year-old right-hander allowed three earned runs on four hits over five innings. He left after 92 pitches and with the Reds trailing, 3-1.
"I liked how he came after their lineup," Cincinnati manager Bryan Price said. "I was pleased by what I saw. Anybody who thinks a kid can come up and throw a complete-game shutout … well that would be a rarity.