19. Andrew BaileyPrevious ranking: 16
The 2009 AL Rookie of the Year has a 2.07 ERA and 75 saves in his three seasons, and his third-most similar pitcher through age 27 is Jonathan Papelbon, whom he was acquired to replace. But durability is the question, and he's yet to throw a pitch for the Sox after suffering a thumb injury in spring training. There's still time for him to become a relevant part of the Red Sox' pen, though perhaps not as the closer.