Jonathan Papelbon is one of two excellent closers for Boston, helping give the team unparalleled pitching depth.

The Providence Journal / Glenn OsmundsonGlenn Osmundson

BOSTON — The bullpen door opened for the start of the ninth with the game on the line Thursday afternoon.

And out came Jonathan Papelbon.

The fireballing right-hander adjusted his uniform, took a deep breath and trotted to the mound at Fenway Park, intent on closing out a victory for the Boston Red Sox against the Detroit Tigers.

A few minutes later, Papelbon’s work was done. It took him 13 pitches to dispose of the Tigers, overmatching two of Detroit’s top hitters, Carlos Guillen and Pudge Rodriguez, for strikeouts en route to his 11th save in 12 chances in Boston’s 2-1 triumph.

Later, during the “night” portion of the day-night doubleheader Thursday, the bullpen door opened once again in the top of the ninth, the game on the line yet again.

And out stepped not Papelbon, but left-hander Hideki Okajima.

Okajima, using what has become a devastating changeup (the Ok-A-Doke) to go along with his fastball and curveball, set down the Tigers’ dangerous Placido Polanco, Gary Sheffield and Magglio Ordonez on a routine flyout and two harmless ground balls, claiming his second save in as many opportunities in the Sox’ 4-2 win.

There are many indicators of a team’s success. Power. Speed. Defense. Strong bench. Starting pitching. The Red Sox are solid in all categories at this point, big reasons why Boston boasts the majors’ best record at 28-12 and a whopping 9½-game lead over the New York Yankees in the American League East.

But an even greater predictor of future success for the Red Sox is that they have not one dependable closer, but two.

While many teams struggle to find one guy to consistently close out games, the Red Sox feature almost an embarrassment of riches in that department, the two-headed, seal-the-deal tandem of Papelbon and Okajima.

Papelbon, of course, was the more celebrated of the two when the season began.

Papelbon blazed his way to 35 saves last year before a shoulder injury sent him to the sidelines in September. But once he proved he was healthy and could handle the load, he asked for, and was happily granted, a return to the closer’s role after the team had expressed a desire in spring to have him in the starting rotation so as to better monitor his health.

Suddenly, the Sox relaxed, knowing that it wouldn’t be cross-your-fingers time in a close game in the ninth with Boston prepared to audition Joel Pineiro, Brendan Donnelly, Mike Timlin and J.C. Romero for the all-important role.

No longer was there the fear that strong six- or seven-inning starts from the outstanding rotation might go for naught for the lack of a lock-down closer.

And then Okajima arrived. He was less heralded than his fellow Japanese countryman, Daisuke Matsuzaka, but in some ways he has been even more impressive than Dice-K, who seems to be finding his stride.

Okajima surrendered a home run to Kansas City’s John Buck on his first pitch in the majors, and he hasn’t been scored on since. After a scoreless inning in setting up Papelbon for his save Thursday and then another clean inning in notching his own save at night, Okajima’s earned-run average is down to a microscopic 0.44.

Sheffield, one of the game’s top hitters for a long time, went out of his way to say that Okajima was one of the best left-handers he had ever faced.

The best part of Okajima’s emergence, aside from the obvious effectiveness? The fact that because he has shown he can handle any and all bullpen roles, the Red Sox don’t have to overwork Papelbon.

They can still monitor him, being careful with him so he doesn’t suffer a shoulder relapse. They can turn to Okajima with confidence, as they did Thursday, rather than trot out Papelbon for two saves in one day, separated by six hours or so.

Over the course of 162 games, of course, it takes more than a team’s star players to determine whether October playoff reservations will be made.

The contributions from the stars making multimillions of dollars are almost taken for granted. Home runs in the bank. Pitching victories and saves already penciled in. They become givens even before the first at-bat or the first pitch is thrown.

And then there’s the supporting cast. They’re called bench players, or fifth starters, or middle relievers. When all is said and done, those players whose contributions are more than expected can make such a huge difference.

So it is with the Red Sox this season.

Already this season, aside from solid play from the starting group, Boston has reaped productive games from a lot of different sources. Alex Cora comes to mind most easily, for his offense and his smart plays and his impeccable defense at shortstop and second base.

Others have had their moments. Doug Mirabelli has clouted a couple of homers. Wily Mo Pena hit a grand slam in Baltimore. Eric Hinske, meanwhile, was the star of Thursday night’s game with a rally-killing face-smashing diving catch and a game-winning homer. And fifth starter Julian Tavarez pitched a beauty in the opener Thursday.

They are happy role players, thinking they might be able to play more on other teams but smart enough to know this is a team that could win the World Series.

Clearly, the pieces to Boston’s pennant puzzle have been fitting together nicely, even without consistent contributions from guys such as Manny Ramirez and J.D. Drew.

But the tightest pieces are relievers/closers Papelbon and Okajima.

They give the Red Sox peace of mind when the games are tight, shortening it to a 21-out game for the opposition because of their seeming invincibility. They give manager Terry Francona two closing options, a hedge against injury.

They form a duo that is the envy of teams around the majors, and two reasons why even skeptical, fear-the-worst Red Sox fans can already legitimately enjoy postseason dreams.

skrasner@projo.com