ST. LOUIS -- For several years, Mitchell Boggs' career was most often discussed in terms of potential.

Scouts fawned over his natural abilities, while the Cardinals held their belief that Boggs could be an ideal fit in the back end of their bullpen someday. Yet there were years in which reality couldn't catch up with potential.

It finally has in 2012, when after seasons of yo-yoing between levels and roles, Boggs has delivered on expectations. In doing so, he has established himself as one of the premier setup men in the league.

"I feel like I'm pitching the way I'm capable of pitching, and I feel like I'm going to continue to pitch this way," Boggs said. "I can be successful and I've been successful, and I'm going to continue to be successful in this league. I just needed to go out there and not worry about the expectations or the situations, and just worry about the guy that I'm capable of being, and pitching the way that I'm capable of pitching.

"That was my mindset starting in Spring Training, and it hasn't changed during the year. I just try to show up every day, and if I get a chance to pitch that night, I'm going to go out there and be the guy that I'm capable of being. And I think that's good enough."

For the most part, it's been plenty good enough. Sure, there have been hiccups, most recently on Sunday, when a game-tying three-run homer left Boggs to shoulder his first blown save May 25. But the Cards' 56-3 record when leading after seven innings is as much a reflection of Boggs' stability in the eighth-inning role as it is Jason Motte's work as a closer.

In fact, the Cardinals are one of only four National League teams to have two late-inning relievers with ERAs lower than 2.58. Boggs' sits at 2.29, the seventh-lowest ERA among NL relievers with at least 40 innings pitched. Motte has a 2.57 mark.

"He and Motte together really seem like a valuable piece," manager Mike Matheny said. "It just started early on, with [Boggs] getting some confidence. When he had some tough outings early, he bounced right back and stuck with it. He didn't try and reinvent the wheel. I think he's needed this long stretch of success to prove to himself that what he has is not just good enough for him to hang around."

That stretch came from June 14 through Aug. 5, a period in which Boggs made 23 consecutive scoreless appearances. He allowed only two of 15 inherited runners to score during that 20 1/3-inning span as well, and opponents hit just .216 off of him.

The scoreless streak came to an end last Wednesday, though by then, the right-hander had long defined himself as Matheny's primary eighth-inning pitcher.

"All the components were there," Matheny said. "It was just a matter of getting him to believe in himself. Having positive thinking is one thing, but you have to have the results."

Boggs has been building to this point, and he took his largest leap forward between the end of 2011 and the start of this season. Not only did he arrive at Spring Training boasting a refreshed level of self-confidence, but Boggs arrived equipped with a new blueprint.

Believing that he had become too predictable a pitcher, Boggs committed himself to throwing more changeups in Spring Training. He did so with success, and kept the pitch in a prominent place in his repertoire once the season started.

Though Boggs hasn't abandoned his reliance on his fastball-slider combo -- Fangraphs.com notes that 90 percent of Boggs' pitches this season have been one of those two -- the changeup is also there. Boggs has used it the other 10 percent of the time.

That percentage, without context, may not seem significant. However, in 2010-11, Boggs threw changeups approximately one percent of the time. This year, he has found particular success throwing the pitch to left-handed batters, who he previously attacked almost exclusively with his sinker.

"In the past, it was basically a non-factor pitch," pitching coach Derek Lilliquist said of Boggs' changeup. "It was just a matter of him finding a grip that suited him the best that he felt he could execute the pitch with. It's a good pitch for him because it spins like his two-seam fastball, and it's got a good bit of speed differential for him."

"I certainly wanted to make sure I stayed committed to it," Boggs added. "I think I have. It's just been a big plus for me."

His fastball command has been better, too, which has allowed Boggs to better control counts. And then there is the idea of role stability, something Boggs never had until this season.

It was evident early in spring that Matheny had every intention of letting Boggs try to fit into the eighth-inning role. Boggs' need to fill that spot only augmented when Lance Lynn moved into the rotation and Fernando Salas endured a shaky start.

Boggs has since stuck as Motte's predecessor, giving him an opportunity to establish consistency in routine and preparation.

"I think it's helped to have an opportunity to go out there and pitch consistently, and understand what is expected of me," Boggs said. "And to know that I've got the confidence of all these guys in this clubhouse and this coaching staff -- that has made a big difference for me. I certainly feel good, and ... I'm throwing the ball well. And I expect to do that all the way to the end."