The Diamondbacks and Red Sox completed a trade Thursday that sends Byung-Hyun Kim to Boston in exchange for third baseman Shea Hillenbrand.
Kim began his major-league career as a reliever and holds the Arizona record for saves in a season with 36, set last year.
However, the right-hander asked the Diamondbacks for a chance to be a starter and this season has posted a record of 1-5 with a 3.56 earned-run average in seven starts.
He has been hurt by a lack of run support.
"Any time you make a trade you, obviously, have to part with talent to get talent," Arizona senior vice-president and general manager Joe Garagiola Jr. said. "(Kim) has been a valuable part of our pitching staff for the past five seasons.
"We needed to bolster our offence from the right side and we feel we've done that with the acquisition of Shea Hillenbrand."
The Red Sox are still employing a closer by committee approach in their bullpen, but reports say Boston would use Kim in its rotation.
Hillenbrand, meanwhile, has been on the trading block since the winter and the Red Sox have a glut of corner infielders.
He has shared time at third base with Bill Mueller, who has a .382 batting average, and has also spent time at first base with Kevin Millar and David Ortiz.
The Mesa, Ariz., native is hitting .303 with 38 runs batted in and three home runs this season.