Erlin's turn in the rotation at Triple-A Tucson comes on the same day as Richard's, and Erlin had already made a spot-start for Richard on June 1. That was his first career start and win, as he held the Blue Jays to two runs in 6 2/3 innings.
"He's getting to the point now where he's about ready to break through," Padres manager Bud Black said of the 22-year-old.
For Tucson, Erlin was 6-2 with a 5.25 ERA in 12 starts. The Padres' other candidates to make the start included long relievers Tyson Ross and Tim Stauffer.
Ross, who pitched two scoreless innings in Tuesday's 6-2 loss to the Phillies, started the season as the club's fifth starter, and made three starts in April before an injury forced him to the disabled list.
"I don't think it was real prudent for him to make this start and expect him to go even five or six innings, based on pitch count and stamina," Black said about Ross.
Ross has been in bullpen since April and Black said he likes having him and fellow long man Stauffer there.
"I think it was a move to keep a little continuity," Black said.
Jamal Collier is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.