Delgado has made 17 relief appearances this year and his last start came on Aug. 22, 2015, when he filled in as a starter against the Reds.
"We felt like he was going to be the most prepared guy for that moment," D-backs manager Torey Lovullo said. "He's had some extended outings, he's been throwing the ball very, very well. We talk about giving us a chance to win a game and we feel like Randall will do that."
Even in a best-case scenario, the D-backs know that they are going to have to use several relievers to get through the game.