The Diamondbacks recalled Nelson from Triple-A Reno prior to Thursday's 8-2 loss to the Dodgers. He struck out two and worked around two hits in a scoreless inning.
The southpaw was in line to begin the season with Arizona's top affiliate, but Joe Mantiply's shoulder injury resulted in Nelson winning a spot in the Opening Day bullpen. The Diamondbacks are expected to deploy him mainly in low-leverage or middle-innings spots while he's up with the big club.