Roach, 24, has never been so happy to be wrong, as manager Bud Black pulled him into his office on Friday to inform him he made the roster as a reliever.
"This was unexpected," Roach said, smiling. "… In the best way possible."
Roach, who has a plus-sinker and gets a lot of ground balls when he's going well, impressed the staff in Spring Training, posting a 3.00 ERA in 15 innings. Roach can be used in middle and long relief.
Last spring -- his first with the team after being acquired from the Angels in 2012 -- Roach had a 1.93 ERA, but he appeared in only five games before being sent to Minor League camp. This spring, he avoided being cut.
"I came in with a different attitude this spring and working as hard as I can. Last year, there was a lot of hype around me coming off the  trade, and I let it get to me," he said.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.