By Tony Massarotti, Boston.com Columnist

Building a bullpen is an inexact science, they told us. Forecasting the performance of a reliever is extremely difficult. And yet, now that they are coming off a 69-93 season, the Red Sox now seem to be placing a majority of the burden on their rebuilt relief corps.

Spring training officially begins throughout baseball this week, and changes abound at the Red Sox' training facility in Fort Myers, Fla. Boston has a new manager, altered outlook, and revamped roster, the latter of which boasts a relief corps stocked from top to bottom with potentially effective arms.

The most important story line this spring? The health and effectiveness of the relief pitchers. The success of the 2013 Red Sox may very well depend on them.

Success is a relative term, of course, so let's keep this as simple as possible. The Red Sox finished 12th in the American League in starting pitching last season and really have added only Ryan Dempster to what looks like a collection of middle-of-the-rotation starters. Save for the top two spots, the lineup is a mishmash of Nos. 5, 6 and 7 hitters. The only place where the Red Sox have the chance to be truly elite is in the bullpen, where general manager Ben Cherington has added closer Joel Hanrahan and setup man Koji Uehara to a group that includes Andrew Bailey, Craig Breslow, Daniel Bard, Alfredo Aceves, Andrew Miller, Franklin Morales and Junichi Tazawa.

That's nine capable to above-average pitchers - count `em, nine - leaving little doubt as to the Red Sox' plan on the bridge back to respectability:

Stay close during the first six innings. Then try to win it in the last three.

Given the Red Sox' dilemma at the end of last season, their options were relatively limited. The Red Sox saved roughly a quarter-billion dollars in long-term salaries when they traded Adrian Gonzalez, Carl Crawford, and Josh Beckett to the Los Angeles Dodgers in August, but the free-agent market was thin. The Sox placed an obvious emphasis on protecting their minor league talent - at least those players who did not injure themselves cleaning guns - which gave Cherington relatively little of value to deal.

And so, the Sox did the logical (and smart) thing. They signed a cast of non-compensation free agents to fill out the lineup and padded the bullpen. How the latter comes together will likely determine whether the Sox are fifth-place finishers in a more balanced American League East - or whether they are contenders for one of the five AL playoff spots.

Let's repeat that, purely for clarity's sake: no one is saying the Red Sox will make the playoffs. Maybe they will. But they can certainly contend for a spot that will likely require somewhere in the vicinity of 87-88 wins. In baseball's new playoff structure, .500 baseball keeps you in the hunt.

Last year, for example, the Baltimore Orioles made the playoffs almost exclusively on the strength of their bullpen, which had both the most relief wins (32) and fewest losses (11) while finishing third in ERA. Second in all three categories? The Oakland A's, who finished 13th in the AL in batting average, 11th in OPS. The Orioles and A's were among the best in the league in both one-run games and extra-inning games, a direct result of their bullpen strength.

For the Red Sox, the real story here is the adoption of this philosophy, which flies in the face of most everything the Sox have told us during the first 11 years of this administration. Generally speaking, the Sox have preached the value of run differential, the triviality of one-run games. One-run games are a crapshoot, Sox officials told us, and good teams frequently win by larger margins.

All of that makes some sense, certainly, and it should be pointed out that the Sox built their share of strong bullpens during the last 11 seasons. Jonathan Papelbon was a force out of the Boston bullpen during his prime, and the Red Sox often backed him with at least one other reliever capable of closing games. Prior to the 2004 season - albeit after an ill-fated closer-by-committee experiment - the Sox signed righthander Keith Foulke, a previously durable closer who could pitch multiple innings at a time. He should have been the Most Valuable Player of the 2004 World Series.

Still, those Red Sox teams had it all, from deep lineups (with serious thunder in the middle) to a true staff ace. The bullpen was designed to protect leads, not keep the game close, the latter of which now seems to be the Boston objective.

Whether the Red Sox can win this way is open to some debate, though the Red Sox question is whether Sox administrators keen on sabermetrics (like owner John Henry) believe they can win this way. The evidence suggests that Henry and his ilk would prefer a different route. But when you are a team like the Red Sox coming off a 69-93 season, you make do with what you can because beggars cannot be choosers.

And you invest your hope wherever you can.