Corbin allowed one run on four hits in four innings of work Tuesday against the Mariners in a 5-4 victory. Three of his four outings have been impressive.
"I'm certainly not disappointed, but I don't want him to get in a position where he's just happy with what he's done so far," D-backs manager Kirk Gibson said. "He's got to keep pushing to get better and better and better."
Corbin worked on throwing his two-seam fastball in to left-handed hitters and was pleased with his outing.
"I felt good today," he said. "I was able to locate my fastball and I thought I threw some real good changeups today. The three of us are all going out there fighting for [the No. 5 spot], but you have to go out there and just pitch your game and I feel that's what I've been doing."
Steve Gilbert is a reporter for MLB.com. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.