One of the few indisputable truths of baseball is that Mariano Rivera is the greatest closer who ever lived, and that it's completely unfair to compare any active pitcher to him ... so let's go ahead and do exactly that. Trust us, it'll make sense.
Somewhat quietly, Kenley Jansen has been one of the most elite relievers in baseball ever since his 2010 debut -- hard to argue with a career 2.19 ERA and 1.94 FIP -- but he's taken that to an absurd new level in 2015. After missing more than a month with a foot injury, Jansen made his debut on May 15, and so far he's faced 41 hitters.