Collmenter, expected to be the D-backs' fifth starter, allowed three runs on three hits to the Rockies over two innings.
"My arm felt real good," Collmenter said. "It felt good warming up in the bullpen and good out there. It was just a matter of, I guess, executing and taking care of that, as opposed to worrying about my arm."
All the runs came in the first inning. After Dexter Fowler drew a walk to lead off the frame, Jonathan Herrera legged out an infield single and Carlos Gonzalez followed with a three-run homer.
"It felt like I hadn't been on the mound in a while, and I think in the first inning I was little excited, kind of jumpy," Collmenter said. "Really tried to settle that down in the second inning and had a little more success after that."
Collmenter retired the side in order in the second.