The announcement was made by Executive Vice President/General Manager Ben Cherington.
Tazawa, 25, has made four scoreless relief appearances for the PawSox this season with one save, striking out nine batters with just two walks and five hits allowed over 7.0 innings. He returned to the Red Sox last September for his final three outings of 2011 after beginning the year on the 60-day disabled list recovering from 2010 Tommy John surgery. Signed by Boston as an international free agent on December 3, 2008, Tazawa is 2-3 with a 7.31 ERA (23 ER/28.1 IP) in nine career Major League games for the Red Sox, including four starts in 2009.
Melancon went 0-2 in four relief appearances for Boston this year, allowing 11 runs over 2.0 innings. Acquired from Houston on December 14, 2011, the 27-year-old is 10-7 with 20 saves, a 4.03 ERA (51 ER/114.0 IP) and 99 strikeouts in 110 Big League appearances, all as a reliever, with the Yankees (2009-10), Astros (2010-11) and Red Sox (2012).