"Delgado was up here and got his feet wet this year, went back down worked on some things, threw a good game, [had] better command and he's the guy," D-backs manager Kirk Gibson said.
Delgado will take the place of Tyler Skaggs in the rotation. Skaggs was sent to Reno last Monday when the team added Charles Brewer to bolster a tired bullpen.
Josh Collmenter was thought to be the frontrunner to make the start, but Gibson decided he was more valuable in his long-relief role.
"He's really good at what he does, you could say arguably as good as there is," Gibson said of Collmenter. "You get into an extra-inning game, you put Collmenter in there and he's won three of them for us. He's done his job. I think, ultimately, if you moved him into a starter's role, then you had to take someone to fill his role and then you're filling two roles and here we're just filling one."
Gibson would not commit to Delgado past Tuesday's start. Due to the rule that says an optioned player must remain in the Minor Leagues for 10 days after being sent down, Skaggs is not able to be recalled until Thursday at the earliest.
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.