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It's no coincidence that the Yankees have had both Mariano Rivera and a consistently strong bullpen for the last 18 seasons. When you've got the G.O.A.T. out there closing down the 9th inning, that makes the rest of the 'pen much easier to construct. The Yankees have excelled at constructing strong support staffs in front of Mo in his time as closer, through free agency and their own farm system, and with Mo finally deciding to show mercy on the rest of baseball and retire after the 2013 season, that support staff was going to be put to the test as part of a transitional period to a new era of Yankee relief pitching.
As usual, the Yankee 'pen wasn't short on depth in 2013. In fact, they had more viable options than available spots near the end of Spring Training. What it didn't have was the strong depth of talent that it usually does and the end result for the group in Mo's final season was a step down from what we've come to expect.
A perfect example of that step down in talent was the change in the long relief role. Early injuries forced David Phelps into the rotation, and his long relief duties were bestowed on rookie Adam Warren. After a strong spring and solid first few appearances, Warren looked like another potential undervalued arm in the same mold as Phelps in 2012. The longer the season went on, the more Warren struggled and regressed back to the mean. He turned in a few more very good long relief outings, but he got roughed up over a major stretch of the summer and his 4.34 FIP, 3.52 BB/9, and 0.0 fWAR were more telling of how his overall body of work looked than his 3.52 ERA.
Another area that took a big hit was the 6th-7th innings. The Yankees were counting on their pair of hard-throwing right-handers returning from injury - Joba Chamberlain and David Aardsma - to shoulder the bulk of that load with Sour Puss gone and D-Rob moving back to the 8th. Aardsma was inconsistent in Spring Training and ended up getting axed because of it. His workload was passed onto Shawn Kelley, who was acquired in a small offseason trade, and Kelley handled it pretty well before injuries and fatigue hurt him late in the season. He pitched to a 3.63 FIP in 53.1 innings and struck out an impressive 71 batters (31.3% K rate). Joba, however, didn't hold up his end of the bargain and was dreadful as the other bridge reliever. He pitched to a 5.64 FIP, gave up 8 HR and 26 BB in 42.0 IP, and his -0.6 fWAR made him the worst reliever on the staff by that measure. The time he missed with injury was soaked up by another rookie, Preston Claiborne, who, like Warren and Kelley, faded in the second half.
Boone Logan was once again tabbed as the primary lefty reliever out of the 'pen, and despite some early concerns about his pitching elbow and durability he was able to fill the role admirably. Joe wisely limited Logan's workload from last year and Logan responded by holding opposing lefties to a .215/.274/.377 batting line (.281 wOBA) with 34 K in 21.0 IP. Because his exposure to right-handed hitters was limited, the damage they did off him was less severe than in years past. A free agent to be like Joba, Logan likely played his last season in New York and he turned in another good one.
Which brings us to the 8th and 9th innings, the 2 innings that Joe didn't have to worry about this year. David Robertson was a stud again as Mo's setup man, pitching to a 2.04/2.61/2.60 slash with 77 K in 66.1 IP and a bullpen-leading 1.6 fWAR. He didn't get many chances to audition for the closer role next year, but by now there should be no doubt about his ability to step into the role in 2014. When D-Rob was doing done his thing, he turned the ball over to Mo, for the final year in his career, and Mo picked up right where he left off before his ACL injury in 2012. 2.11 ERA, 44 saves, a mere 9 unintentional walks in over 60 innings. It was vintage Mo and a much more fitting ending to a fantastic career.
Consistent late-inning dominance and shaky middle relief. That was the Yankee bullpen in a nutshell in 2013. The final iconic image of Mo embracing Andy Pettitte and walking off the Yankee Stadium mound to a standing O serves as the jumping off point for next year's bullpen, when there will be a lot of work to do and a lot of spots to fill to rebuild. The Yankees bullpen took a step back in 2013, just like the rotation, and they're losing the most important piece of it. Time well tell how much the loss of Mo will really affect the 'pen moving forward, but at the very least we all got the privilege of watching him work his magic one more time.