A first-time All-Star in 2013, Mujica posted a 2-1 record with 37 saves and a career-best 2.78 ERA (20 ER/64.2 IP) in 65 relief appearances for the National League Champion Cardinals during the regular season. He ranked fifth among NL leaders in saves and ninth with 49 games finished.
The 29-year-old Mujica struck out 46 batters while issuing only five walks this past season. His 9.20 strikeout-to-walk ratio led all National League pitchers (minimum 15.0 IP) and was second in the majors only to Koji Uehara's 11.22 mark. He also averaged the fewest walks per 9.0 innings (0.70) among any pitcher who threw at least 10.0 innings in 2013.
A native of Venezuela, Mujica was originally signed by Cleveland as an international free agent in October of 2001 and has appeared in 381 major league games over parts of eight seasons with the Indians (2006-08), Padres (2009-10), Marlins (2011-12), and Cardinals (2012-13), with all but four outings coming in relief. He has posted a 19-19 career record with 41 saves, a 3.75 ERA (183 ER/439.1 IP), 350 strikeouts, and 68 walks.
His 5.15 career strikeout-to-walk ratio is tops in major league history among hurlers with at least 400.0 innings pitched and he also has the lowest average of walks per 9.0 innings among active pitchers with at least 400.0 innings at 1.39.
Since the start of the 2009 season, his 352.2 relief innings rank second in the majors behind Tyler Clippard's 383.1 frames. In that time, he ranks second among major league relievers with 1.35 walks per 9.0 innings, trailing only Uehara (1.07), and is fifth in that group with a 5.43 strikeout-to-walk ratio.
Mujica has appeared in 11 career postseason games, all with St. Louis over the last two years, going 1-0 with a 2.79 ERA (3 ER/9.2 IP).
With the acquisition of Mujica, the Red Sox' 40-man roster is now at 40.