AaronGleeman.com

When closer Joe Nathan left Saturday's spring training debut with pain in his surgically repaired elbow the Twins hoped it was merely scar tissue breaking up, but after flying back to Minneapolis for an MRI exam he's been diagnosed with a torn ulnar collateral ligament. Nathan is expected to rest for a couple weeks in an effort to find out if can possibly pitch through the pain, but more likely than not he's headed for season-ending (and at age 35, perhaps career-threatening) Tommy John surgery.

There's no getting around the fact that losing Nathan would be a huge blow to the Twins. Since arriving in 2004 as part of the famed A.J. Pierzynski deal he's been arguably the best reliever in all of baseball, saving 246 games with a 1.87 ERA and 518 strikeouts in 418.2 innings spread over 412 appearances. During that six-season span Nathan's adjusted ERA+ of 236 is the best of any pitcher with 300 or more innings, and Mariano Rivera at 234 and Billy Wagner at 202 are the only others above 200.

Nathan is irreplaceable because no other reliever will be able to match how consistently fantastic he's been with yearly ERAs of 1.62, 2.70, 1.58, 1.88, 1.33, and 2.10. He is not, however, irreplaceable simply because of the role he filled. Closers are made, not born, and despite what you may hear from people looking to build the role up into some kind of mythical test of wills the primary characteristic needed for handling ninth-inning duties is being a good pitcher. Period.

Nathan has been a great closer, but before that he was a starter moved to the bullpen because of arm injuries and had just one season as a setup man. Eddie Guardado was also a failed starter who spent a decade as a middle reliever before getting a chance to close, and then saved 86 games in two years. Rick Aguilera is another former starter turned reliever, and was 27 years old before recording his first save. Being an established closer isn't a prerequisite for being a successful closer.

Losing a great pitcher like Nathan hurts because the Twins don't have an equally great pitcher to take his place, not because the role he filled is much too vast and important for a mere mortal. Nathan was a mere mortal before assuming the role, as were Guardado, Aguilera, and so many other top closers. Nathan has converted 90.7 percent of his chances with the Twins, which is amazing, but the MLB-wide success rate for all closers is 86.5 percent and all but the disasters are usually around 80 percent.

Nathan has had 45.2 save opportunities per year and by converting 90.7 percent of those chances he's averaged 41.0 saves. An "average" closer converting 86.5 percent would have 39.1 saves and a "poor" closer converting 80.0 percent would have 36.1 saves. Per season that equals 1.9 fewer saves at 86.5 percent and 4.9 fewer saves at 80.0 percent. And it's important to remember that not every blown save ends in a loss, so being without Nathan will likely cost 3-4 wins including his work in non-save spots.

Ron Gardenhire hasn't dropped any hints about the replacement closer because he's still holding out a slim hope that Nathan can pitch through the injury, but bullpen depth was one of the Twins' strengths coming into spring training and he has several decent options from which to choose. I'd likely go with a closer-by-committee approach based on matchups, at least initially, but my guess is that Gardenhire's preference is to find one man for the job even if it takes giving a few guys tries before settling on him.

Matt Guerrier has been setting up Nathan for the past six seasons, with a 3.31 ERA in 389 innings as a reliever, but his raw stuff isn't exactly overpowering and more importantly his valuable ability to make multi-inning appearances or rescue other pitchers from mid-inning jams would likely cease given how Gardenhire has used his closer. In terms of raw stuff Jon Rauch is much more similar to Guerrier than Nathan even if standing 6-foot-11 with neck tattoos makes him look like a closer.

With that said, Rauch has more closing experience than the rest of the fill-in candidates combined and even if that basically amounts to just 17 saves with the Nationals two seasons ago I'll be surprised if it doesn't play a big factor in Gardenhire's decision making. Rauch as a closer is obviously far from ideal, but he has a 3.59 ERA in 363.1 innings as a reliever, including a 3.60 mark last year, and was indeed right "around 80 percent" when given regular save chances in 2008.

Jose Mijares had a good rookie season with a 2.34 ERA in 62 innings and was often billed as a future closer while coming up through the minors thanks to raw stuff that sits a step above guys like Guerrier and Rauch, but Gardenhire seems unlikely to trust a second-year pitcher in the ninth inning right away. Mijares also allowed right-handers to hit .283 with a .791 OPS last year while completely shutting down fellow lefties, so for the short term at least he's probably best suited for a semi-specialist role anyway.

Once upon a time Jesse Crain was also thought of as a future closer and still has the mid-90s fastball for the job, but he's hardly been consistently reliable even as a setup man and spent six weeks of last year at Triple-A following a midseason demotion. Setting aside whether Crain could handle closing I'd be shocked if Gardenhire trusted him enough to give it a try, which is also why prospects like Anthony Slama and Robert Delaney aren't realistic options.

Francisco Liriano may be an intriguing closer candidate, but if he looks good this spring the Twins will want him in the rotation for 200 innings rather than the bullpen for 70 innings and if he isn't impressive in camp they surely won't be handing him late leads. Pat Neshek emerged as Nathan's top setup man in 2006-2008 with a 2.91 ERA and 142 strikeouts in 121 innings and might be the leading candidate to step into the job if not for the fact that he's coming back from a Tommy John surgery of his own.

Neshek's recovery is said to be going well and his spring training debut last week was promising, but he hasn't thrown a regular-season pitch since May of 2008. Tossing him right into the ninth-inning fire is highly unlikely and probably ill-advised. And while his vulnerability to left-handed batters was grossly exaggerated before the surgery he certainly benefited from being used in spots that weren't heavy on lefty sluggers. He'd benefit from that now more than ever, but it isn't doable for a one-inning closer.

Before the surgery Neshek would have been my choice to step in for Nathan and even after the surgery if healthy he'd be a good fit in a closer-by-committee situation with Mijares, but with his status up in the air and no need to rush him into anything it's a moot point. And of course Gardenhire is unlikely to use multiple, matchup-based closers anyway. At some point pining for Mijares, Neshek, or Mijares/Neshek could make sense, but for now Gardenhire may lean toward Rauch and I'd find it hard to disagree.

Whatever happens the bullpen's depth has the Twins remarkably well-positioned to handle losing their stud closer and any decision Gardenhire makes will likely result in less of a game-saving dropoff than most people seem to think. Nathan has been spectacular, but the role he's filled is so rigid and fawned over that the gap between truly "great" and merely something resembling "mediocre" in the ninth inning is typically overstated and often unpredictable, with last year providing a pair of prominent examples.

MLB's best save percentage belonged to Fernando Rodney, a 32-year-old career-long setup man with a 4.28 ERA who went 37-of-38 for Detroit. Philadelphia won 93 games and the NL pennant despite one of the worst closer seasons ever by Brad Lidge, who went 0-8 with a 7.21 ERA and MLB-high 11 blown saves. Nathan's injury drops the Twins' playoffs chances, which is difficult to stomach after a productive offseason had the team looking so strong, but they can definitely survive and even thrive without him.

And maybe the Twins will stumble upon their next great closer in the process.