He showed last season he deserved it. He got 30 starts at first base, 22 at third, 13 in the outfield and the two at second. He played all of them reasonably well, but what he did that forced St. Louis to look for a spot was hit.
He led NL rookies with a .365 on-base percentage. His 11 pinch-RBIs were the second-most in the NL. He also had a .294 batting average, five doubles, six triples, 46 RBIs and 34 walks in just 296 at-bats.
When the season ended, Cardinals manager Mike Matheny asked him to work on playing second exclusively next season. Carpenter called it "a homework assignment."
"It was: 'We think you might be able to do this. So take some ground balls. Go work on it and see what happens,'" Carpenter said.
He poured himself into it, splitting his workouts between a Houston fitness facility and the University of Houston, where one of his college coaches, Todd Whiting, had taken over the program.
"It's not an easy transition to make," Matheny said. "All those things you just never know about a player until you see him on an everyday basis. You see hands. That's the first thing. And his athleticism. The one thing that seemed pretty obvious to us is the fact he's a tireless, relentless worker. You mix that with the ability and conscientiousness and attitude, and you set yourself up for a pretty good result."
Carpenter reported to Spring Training early for some hands-on work with Cardinals coach Jose Oquendo. There were things he could practice and things he couldn't. But by the time the Cardinals finished Spring Training, there was a reasonable level of confidence that Carpenter had found a home in the lineup and the top of the batting order.
"He's got good natural movement," Oquendo said. "We hit 'em right at him, moved him side to side. He had no problem. He has done a great job. He catches the ball. He turns double plays real well. The hardest part is the mental part, the timing, and he's working every day on that."
As far as hitting, well, Carpenter has made that part of it look easy.
"I've been really happy with the way I've been able to adjust as a second baseman," he said. "I don't want to say I always knew I could hit, but I felt like I had a pretty good idea how to hit. Defensively, that's the thing I've been most proud of -- learning a new position at the big league level. I can still get better, and I'm working at that every day."
Carpenter is leading NL second basemen in on-base percentage (.396) and on-base-plus-slugging (.863). He's second in batting average (.318), third in walks (25) and fifth in home runs (6).
He has the highest Wins Above Replacement number (3.4) among all NL second basemen, 10th-highest in the NL overall. Four other NL second basemen -- Marco Scutaro (19th), Chase Utley (43rd), Brandon Phillips (45th) and Neil Walker (53rd) -- are far behind.
"He has done a tremendous job," Cardinals first baseman Allen Craig said. "We all know he can hit. He has done a great job at second base and at the top of our lineup. He's a gamer. He's a guy you want out there, just a consistent player. He brings the same type attitude to the field every day."
He grew up the son of a successful Houston high school baseball coach, Rick Carpenter.
"Growing up around a baseball field, having a father figure who knows the game, who is a successful coach, I was around winning teams and know what it takes," Carpenter said. "All those things that are valuable had a huge impact on my career."
That he finally has arrived has more than made up for some disappointment along the way. He blew out his elbow during his junior season at TCU and was not drafted. He returned for his senior season, and St. Louis got him in the 13th round of the 2009 First-Year Player Draft.
He's one in a long list of smart Draft choices made when Jeff Luhnow, now the general manager of the Astros, ran the draft for the Cardinals. Specifically, he was the 26th of the 48 Luhnow picks that have played in the big leagues.
"It wasn't until his senior season at TCU, his fifth year, that he put together a pretty good season," Luhnow said. "It was a combination of the area scout who liked him and the analytics that loved him. When those two things intersect, typically an organization like the Cardinals are there to take advantage of it."
For Carpenter, the whole thing has been a "blast." He's a big part of the team with baseball's best record and playing with a large number of other homegrown Cardinals, many of the same guys with whom he advanced through the system.
In the end, it couldn't have worked out better.
"Just to be up here on a great team is fun, but then to get in there and have an opportunity to play every day is a real blessing," he said. "I've really enjoyed it. It's been really fun competing on a great team like we've got."