Jim O'Connor-USA TODAY Sports
1. Luke Gregerson, San Diego Padres (68.5%, 82.9 MPH, 15.2 wSL, 1.82 wSL/C)
One of the few pitchers in the league today who throws primarily sliders, Gregerson throws the pitch as much as anyone in the game, and he's been a lights-out setup man as a result.
In five seasons with the Padres, he's made 298 appearances, posting a 2.90 ERA and 1.104 WHIP and striking out 295 in 289 innings. He pitched for the U.S. in the World Baseball Classic and is undoubtedly one of the premier setup men in the league today.
2. Sergio Romo, San Francisco Giants (61.0%, 77.8 MPH, 15.3 wSL, 2.69 wSL/C)
When Brian Wilson went down with a season-ending injury early last season, the Giants turned to a closer-by-committee. However, it didn't take long for Romo to emerge as the man in the ninth inning, and once he did he went on to convert 14 of 15 save chances.
He doesn't have the prototypical power slider that many closers do, as the pitch is roughly 10 miles per hour slower than his fastball, but that doesn't make it any less effective an out pitch for him.
3. Matt Harvey, New York Mets (13.9%, 88.4 MPH, 5.7 wSL, 2.97 wSL/C)
It may be a bit early to put Harvey this high on the list, and I'm not saying I based the ranking on Internet GIFs, but just look at this and this.
Harvey throws his slider as fast as anyone in the league, as it is a true wipeout slider in every sense of the word. The 24-year-old is off to a phenomenal start to his career, and his fastball/slider combination is largely to thank.
4. Craig Kimbrel, Atlanta Braves (31.4%, 85.7 MPH, 11.3 wSL, 3.46 wSL/C)
Not to generalize, but nearly every pitch that leaves Kimbrel's hand has the potential to rank as one of the best pitches in baseball, and while his blazing fastball is his go-to pitch, his slider isn't half bad either.
He throws those two pitches almost exclusively, and they have allowed him to lead the league in saves each of the past two seasons while striking out 293 hitters in 168 innings over the course of his career.
5. Clayton Kershaw, Los Angeles Dodgers (22.7%, 85.3 MPH, 5.1 wSL, 0.58 wSL/C
Kershaw used to rely on his curveball far more, and it is still a filthy pitch when he decides to snap one off, but it is the slider that he leans on now, and the development of the pitch has been a big reason for his success over the past two seasons.
He began throwing the pitch more frequently at the start of the 2010 season, and since then he's gone 50-26 with a 2.53 ERA and 9.3 K/9, while winning back-to-back ERA titles. While his slider may not be as overpowering as those of the above guys, he relies on it for success as much as anyone in the league.
*Braves reliever Jonny Venters may have the most dominant slider in all of baseball when he's on, but he was inconsistent last season and has yet to pitch in 2013 as he battles elbow problems, so he was left off this list for now.