Who is the best reliever in baseball over the last two years? If we made a list, the usual suspects would shoot straight to the top. Craig Kimbrel is a given, Koji Uehara was essentially unhittable for one calendar year, Kenley Jansen skews “untouchable” and Aroldis Chapman is in his own world. Greg Holland and Wade Davis surely jump to mind without much searching, Sean Doolittle and David Robertson deserve attention for their high-leverage work.

There is one reliever that is conspicuously absent from that list (because I excluded him!) but since the start of the 2013 season, this closer boasts some unbelievable numbers. Pitching to 41 ERA- (fifth best among qualified relievers) and a 51 FIP- (third) while posting roughly 5 RA9-WAR and 4 fWAR, both of which place him among the elite stoppers in baseball.

The reliever in question is Mark Melancon, the setup guy-come-closer for the Pittsburgh Pirates. Melancon went from being well-traveled to a brief sting in AAA to become the very best of a stout group of relievers holding the Pirates in the playoff race for the second straight season.

Earlier this month, our own Dave Cameron pointed out that the Pittsburgh Pirates, off all teams, claim the best offense in baseball this season. Their starting pitching doesn’t quite measure up, as their reclamation projects in 2014 aren’t faring quite as well as last year and Gerrit Cole missed a few months with an injury. Pirates starters rank dead last in WAR and in the bottom five for RA9 WAR. They’re bad and yet here the Pirates sit, holding down the second NL Wild Card spot with a 77-69 record.

In the face of this extra workload and additional pressure to perform, the Pirates bullpen stands tall, none more so than Melancon. Another terrific season in which he refuses to give up free passes or allow home runs (a 4% walk rate and just 0.28 HR/9 allowed this season), all while netting copious ground balls (more than 55%, down from 60% in 2013.) Melancon has become a rare type of two-pitch reliever, offering mostly cutter/curve in a sinker/slider world.

The cutter gave him a weapon against left-handed batters, missing both barrels and bats while his command of the pitch keeps him ahead in the count and sets up his power curve, always a weapon for the former Yankee, Astro, and Red Sock. Despite learning from Mariano Rivera early in his career, Melancon played with his cutter grip for years before discovering one that felt comfortable and struck the balance between movement and velocity.

Whatever Melancon’s doing is working. He’s allowed just three home runs since joining the Pirates, one in 2013 and two in 2014. Two of those came against left-handed hitters, combining with lefties mere four doubles against him to create one of the pitchers in baseball for glove-sided batters to hit hard. Is it all about the cutter? What is the key to Melancon’s success against lefties?

Melancon throws his cutter as the first pitch against lefties about 80% of the time. But rather than backdoor it, the pitch is largely delivered over the plate or on the inside half. According to Baseball Savant, only Kenley Jansen throws a higher percentage of his cutters inside to lefties. It depends on the hitter, of course. Thursday night, Melancon faced Chase Utley with two runners on base in a save situation. He started the Phillies star with two cutters on the outside half before dropping in a curveball (which Utley fouled back). With the count 1-2, the Pirates reliever opted for a cutter inside and under Utley’s hands for the swing and miss. The next batter was another lefty, outfielder Grady Sizemore. Melancon went right after him, throwing a cutter on this inside half that Sizemore popped into foul ground to end the game.

The inside cutter is difficult to do much of anything with, unfortunately for batters. Staying inside the ball and going the other way is an option but a task much easier said than done, especially with Melancon sitting around 92 mph. His excellent command (and the strong framing work of his primary catcher) puts the pitch in the strike zone more often than not, dropping batters in a 0-1 hole that brings his curveball into play.

The power curve was always a great weapon for Melancon, going all the way back to his days as a Yankees prospect. Melancon’s power curve averages 81.4 mph, making it one of the harder deuces among current relievers. A platoon-neutral offering like the cutter, the two pitches give Melancon nothing but options but they also work together. While he opts for cutter almost exclusively to start at bats, with two strikes it’s 50/50 as to which pitch he throws.

He isn’t the flashiest pitcher in the league, though his placid exterior won the respect of his teammates, as Melancon serves as a calming presence in the Pirates bullpen. He doesn’t have the same gaudy strikeout rates of some of the higher profile relievers in the game, but Melancon absolutely belongs in their company.

His cutter is among the elite pitches in the game – it keeps hitters off-balance no matter which batters box they occupy. It keeps the ball either on the ground or in the park and, most importantly, when Melancon enters the game the Pirates stay ahead. Tightly holding onto the second Wild Card spot as they are for now, they need everyone of those wins he can preserve.