He has been outstanding for Pawtucket, posting a 1.29 ERA in 10 appearances.
The Red Sox used two of their three lefty relievers (Chris Capuano and Andrew Miller) in the 2-1 loss in Game 1 loss making Britton a logical addition to the roster.
"He's been throwing the ball very well," said Red Sox manager John Farrell. "And he's been stretched out to 40-plus pitches. He adds to our bullpen tonight."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.