If Jonathan Papelbon had his current slider in 2007, this image might not have become so common. (AP)

In 2007, Jonathan Papelbon was being groomed for the rotation during spring training. He’d suffered an almost-catastrophic injury at the end of his spectacular first season as a closer, enduring a shoulder subluxation at the end of the 2006 campaign, and the Sox thought that his long-term health might be better served while working on a five-day routine.

Moreover, Papelbon had made three solid starts to begin his big league career in 2005, allowing just four runs in 16 innings (2.25 ERA) while striking out 15 (and walking 10). The Sox thought that he could be a valuable asset as a member of the rotation.

There was only one problem. Papelbon couldn’t spin a decent breaking ball. He’d tried a slider in the minors, with poor reviews. He was throwing a curveball in big league camp in 2007; the pitch was flat, lifeless and eminently hittable.

Sox manager Terry Francona thought that Papelbon could be a solid starter based on his explosive mid-90s fastball and diving splitter, but the lack of a legitimate third pitch would limit his value in the rotation. He would see too many pitches fouled back, see his pitch counts run too high, to get deep into the game.

“I think that was the concern I had,” acknowledged Francona. “I looked at him more as a two-pitch pitcher and maybe a guy who would have to work so hard to get through five. I never thought he wouldn’t be successful or get people out, but he’d have to work so hard to get through five that all of a sudden he’s not going deep in games. He’s too good a pitcher. I always thought he could impact us better in the bullpen.”

It was a role, of course, that has suited Papelbon well. He has become one of the game’s elite closers, having made four All-Star teams, mostly on the strength of that fastball and splitter.

Even so, Papelbon didn’t give up on the idea of a third pitch over the years. He continued to refine a breaking ball, and in the last three years, he has worked hard to refine his slider. At first, Francona was skeptical of the pitch.

“I remember when he first broke it out, I was like, ‘Pap, don’t ever get beat with that pitch. Just put it in your back pocket and just go fastball split,’” said Francona. “[But] it’s become a viable pitch.”

Even so, as much attention as the slider has drawn, it remains the Sox closer’s third pitch. Francona feels that the right-hander’s success is still primarily a function of his fastball mechanics and his splitter, something that was evident in Papelbon’s second save of the season on Saturday.

“Last year, there were times when that fastball would wander a little bit. He’d get himself into situations where he had to work so hard to get through an inning. Now the fastball and the splitter are coming out of the same slot,” said Francona. “You saw it yesterday — he got ahead with fastballs, the count went to even, and then he threw a split and it was right out of the same fastball motion and he got a swing and miss. That’s when he’s really effective. He’s mixing in his breaking ball, but when his fastball-split are locating, he’s good.”

Interestingly, Papelbon has used the slider more than the splitter in the early going this year. He has thrown his splitter nine times (getting three swing-and-miss strikes with it), compared to 18 sliders (which have also produced three swings and misses). He has put up impressive numbers by using his three-pitch mix thus far, with a 1.80 ERA and eight strikeouts (against two walks) in five innings.

That the slider has become such a significant part of his arsenal raises a somewhat fascinating notion. Had Papelbon had such a breaking pitch in spring training in 2007, the Sox may have had a different decision to make regarding his long-term viability for the rotation, something that Francona acknowledged. That said, the team and the closer himself have no regrets about the path that his career has taken, given that he was a central part of the Sox’ World Series run in 2007 and their subsequent successes.

“He’s done OK,” mused Francona. “He’s done OK right where he’s at.”