Rosario, 27, was designated for assignment by the Athletics on Nov. 30 after being acquired from Boston two days prior in exchange for a player to be named later (RHP Graham Godfrey). Rosario had been claimed by Boston off waivers from the Miami Marlins on Oct. 17.
The right-hander posted a 1.04 ERA with 16 saves and 24 strikeouts over 26 innings in 25 appearances for Miami’s Triple-A club in New Orleans in 2012. In addition, he made six outings between High-A Jupiter and Double-A Jacksonville last season, including four on rehab. Rosario also appeared in four major league games with Miami in 2012, allowing six runs over three innings. This offseason, he pitched in the Dominican Winter League.
Originally signed as an international free agent in 2004, Rosario has compiled a 30-18 record with 47 saves, a 3.15 ERA (137 ER in 391.0 IP) and 403 strikeouts over 181 career minor league outings in the Marlins system, including 35 starts.
The Red Sox's 40-man roster is now at 39.