It's an unfamiliar role for Pennington and he is experimenting with what he needs to do to stay sharp between starts.
"I'm still working on that part," he said. "Until a couple of weeks ago, I had never not played three days in a row. It's a different mentality. It's still preparing yourself for the game, but trying not to over grind it and overdo it just because you have time to tinker."
Pennington has a good model in teammate Eric Hinske, who has made a living the past few years of coming off the bench.
"I've definitely watched him and talked to him about what he does, because he's got a very specific role and job and he's very good at it," Pennington said. "Mine's a little different because I have to prepare for defense too or baserunning or something like that, plus I come in earlier [in the game] than him. You've got to be ready for one specific moment of the game and it's usually a pretty big moment."
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.