The most important pitching change of the 2007 season for the Boston Red Sox may have already been made.

The persistent, pesky question with no answer now finally has one: This year’s closer will be last year’s closer – Jonathan Papelbon.

At most, Terry Francona’s call to the rotation should greatly strengthen the team’s only significant weakness – the bullpen – without severely weakening his starting staff. At least, it will significantly cut down his Rolaids intake and sheep counting as the unsettled bullpen situation has – Francona admitted – caused him some sleep loss.

As much as the bullpen is almost always a source of springtime distress for most managers, it has been even more so for Francona, especially with a gaping void at closer and Mike Timlin’s oblique muscle strain.

With Timlin starting out on the disabled list, Boston’s bullpen needed some good news. If the shoulder soreness that shut Papelbon’s 2006 season down a month early is indeed a thing of the past, then the intimidating righthander’s return to closing is the best news possible. It should also hearken a shift in the American League eastern division’s balance of power away from nine-time defending champion New York.

The Red Sox open their season on Monday at 4:10 p.m. in Kansas City against the Royals.

Starting out strong

The Red Sox rotation was already being hailed as arguably one of the two best in the majors along with Detroit’s. Will it be weakened by Papelbon’s absence? Probably. Will it still rank among the best in baseball? Possibly.

While Papelbon’s switch affects the overall talent of the Sox starting pitching, it doesn’t affect its depth. Don’t forget that a healthy Jon Lester and an enigmatic-yet-talented Matt Clement wait in the wings if injuries strike or Julian Tavarez, Papelbon’s rotation replacement, falters.

The rest of the rotation is at least solid if not spectacular. Yes, two of the starters are 40 years old, but when one relies on location and the other relies on guile rather than speed or power, age isn’t as much of a worry. In Curt Schilling, Daisuke Matsuzaka, Josh Beckett, Tim Wakefield and Tavarez, the Sox have a potent mix of experience, talent, youth, leadership, and variety.

Schilling has looked solid all spring and is certainly motivated as this is the final year of his contract. The 40-year-old righty arguably has the best location skills in the majors.

In Matsuzaka, Boston has an already accomplished 26-year-old who doesn’t have the pressure of trying to carry a club and boasts SIX major league pitches that scouts grade out as “plus.” Will there be growing pains or tough lessons? Yes, but Dice-K appears to be a good student who doesn’t need a lot of extra instruction.

When the knuckleball is knuckling as it should, Wakefield, 40, is almost unhittable and a source of maddening frustration for opposing sluggers. His floating, slow-motion signature pitch and deceptive release offer a stark contrast to the power pitching of which Schilling, Beckett and even Matsuzaka are capable.

Beckett, 26, has extra motivation this season to go along with a year’s worth of familiarity with American League hitters. Both should help the former Florida Marlin lower his ERA of 5.01 and his career-high total of 36 home runs allowed last year while equaling or improving his 16-win total.

Tavarez, 33, gets his wish and remains a starter, which he became on Aug. 31. Lost in the anguish of Boston’s third-place division finish was the fact the righthander was unbeaten with a 3-0 record and 4.01 ERA in six starts last fall.

Lining them up

Boston’s offensive production should be noticeably improved with the addition of speedster Julio Lugo to the top of the batting order and productive (when healthy) J.D. Drew to the middle of it.

Lugo should be the catalyst in the leadoff spot that the Sox expected Coco Crisp to be last season as well as a disruptive presence on the basepaths. Drew should provide protection for sluggers David Ortiz and Manny Ramirez as well as more offensive punch and reliable on-base presence in the No. 5 slot. Ortiz is a lock in the No. 3 spot, as is Ramirez at cleanup.

There are many exclamation points, but several question marks as well in this lineup. Any variety of things could happen, but just for example, here are the best- and worst-case scenarios to keep in mind:

Best-case – If Drew stays healthy, Ramirez stays somewhat focused, Jason Varitek figures out how to “fine-tune” his hitting for the better after a spring training-long slump, Dustin Pedroia reverts to a patient approach at the plate, and Coco Crisp can return to his 2005 form, the Sox could make a run at the record-breaking numbers put up by the 2003 Sox. That is especially true with two speedsters at the top and bottom of the lineup and three deadly bats in the middle.

Worst-case – If Drew fails to play more than 110 games for the fourth time in the last seven years, Manny decides he’s unhappy again, Varitek fails to figure out what adjustments he needs to make and carries his spring slump through the season, Pedroia continues to swing for the fences, and Crisp’s batting average continues to wilt, Boston’s $200 million-plus offseason shopping spree will look like the biggest waste of money since the Pentagon was buying $200 hammers and $500 toilet seats.

Putting them on the defensive.

What was arguably Boston’s best defensive infield in the modern age is no more. Sure-handed second baseman Mark Loretta signed with Houston, defensive wizard Alex Gonzalez is now Cincinnati’s shortstop. Youkilis and gold-glover Lowell are back at first and third base, respectively, and Varitek is still one of the game’s best overall catchers, but infield defensive skill goes from noticeable strength to gray area at best.

Replacing Gonzalez with Lugo, a player known more for his bat and speed than his glove work, is a net loss defensively. Pedroia, who was known for his defensive ability throughout college and in the minors, has big shoes to fill at second base, but the 5-foot-9, 180-pound rookie dropped 15 pounds in the offseason to increase his defensive range and says he feels both stronger and quicker.

The outfield looks better overall this season with the addition of Drew in right field. Drew brings a more powerful and accurate arm than blue-collar guy Trot Nixon, and he could be a major improvement offensively as well as long he enjoys good health. Ramirez may be known for his defensive indifference, but he led the team in outfield assists last year and has become a solid left fielder. Having a guy who can play all three positions and bring a power bat to the lineup like Wily Mo Pena as a backup gives the Sox an added bonus most teams don’t have.

Finishing touches

The bullpen still looms as a potential weakness with Timlin starting off on the disabled list, but the addition of Brendan Donnelly via trade as a situational righthander should strengthen it. And the springtime performances of lefties J.C. Romero, in particular, along with Hideki Okajima and Javier Lopez could give Francona situational flexibility few managers have had in recent years. Righthander Joel Pineiro may flourish as Papelbon’s setup man now that he is no longer under the microscope as his replacement and, if healthy, Timlin is both a steadying presence in the clubhouse and a strong one on the mound. One of the more intriguing guys to watch is 6-8 righty Kyle Snyder, who was too impressive to let go in spring training, thereby leading to his conversion from starter to long reliever.