It’s easy to forget now, but Adam Warren only made the Opening Day roster in 2013 because Phil Hughes suffered a minor back injury late in Spring Training. Hughes went down, long man David Phelps had to step into the rotation, and Warren got the long relief job almost by default. Warren pitched well and stayed on the roster even after Hughes returned. (Cody Eppley went down instead.)
Since then, Warren has developed into a pretty important piece of the pitching staff. He was the long man back in 2013, a setup man in 2014, and now a starter early in 2015.