The Red Sox acquired left-hander Fabian Williamson from the Mariners in exchange for right-hander David Aardsma on Tuesday.
Williamson spent the entire 2008 season with Class A Pulaski, compiling a 4-3 record with a 4.10 ERA in 52 2/3 innings and 11 starts. The 20-year-old's 67 strikeouts ranked fifth in the Appalachian League. In his two seasons in the Minor Leagues, Williamson -- selected by Seattle out of high school in the 22nd round of the 2006 First-Year Player Draft -- is 10-5 with a 3.55 ERA in 124 1/3 innings.
"He's a guy we're excited about," Red Sox assistant general manager Jed Hoyer said via conference call. "We had good reports on him. He's a guy who is an athletic left-handed pitcher. He's a 22nd-rounder by Seattle, but he's performed well, and I think it was a situation where we designated David and we were happy to get a quality player in return."
Aardsma, 27, was designated for assignment by the Red Sox on Thursday and went 4-2 with a 5.55 ERA in a career-high 47 relief appearances in '08, his first season in Boston.
Alden Gonzalez is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.