The Pirates designated Pimentel for assignment last Sunday when they set their roster for opening day. The 25-year-old was 1-1 with a 4.91 ERA in nine spring appearances and had a 4.50 ERA in 25 career relief outings for Pittsburgh in 2013 and 2014.
Edwards went back to the minors Sunday, a day after getting recalled and coming out of the bullpen against Houston. Trying to protect a 5-1 lead in the sixth inning, he walked the only two hitters he faced to force in a run.
He pitched in Round Rock's season opener before joining the Rangers.