As a multi-inning reliever, Whitlock hopes to give his team the same spark he did four years ago.

"It's huge," said Red Sox pitching coach Andrew Bailey. "He's a guy that you can hand the ball off to and have him go a couple of innings late in the game and give the back end guys a rest. He's a multi-inning force back there. Gives us another way to finish games. Not only your typical multi-inning guy cleaning up some down games or some big games, he's a guy that can throw multiple innings in close games as well which gives AC a different way to finish ballgames, which is really valuable for us."