Petersen has claimed a spot in the Marlins' Opening Day bullpen, Christina De Nicola of MLB.com reports.
The 31-year-old right-hander did enough this spring to stick around the 26-man roster, producing a 3.12 ERA and 7:3 K:BB over 8.2 Grapefruit League innings. Petersen should handle a low-leverage role after contributing a 4.00 ERA, 1.39 WHIP and 17:7 K:BB in 18 big-league innings last season split between Atlanta and Miami.