The left-handed-hitting Carp is coming off an injury-plagued season in which he hit .213 with six doubles, five homers and 20 RBIs in 59 games.
Carp will compete most directly with non-roster invitee Lyle Overbay to be Boston's backup first baseman behind Mike Napoli. Manager John Farrell has said that defensive versatility -- the ability to play first base and left field -- is preferred.
"It increases the competition, particularly at first and left field," Farrell said of the move for Carp. "We've had a chance to talk to some other guys that might be directly impacted by that. We've been able to add a talented player to camp here -- someone that we've had conversations about throughout the course of the offseason. Finally he became available. [He's] another left-handed hitter that has that versatility on the defensive side."
Overbay took the news like a professional.
"You bring guys in here to win games and to give you options, because you never know those unknowns," Overbay said. "I think that was their biggest thing, is playing outfield and first base. I think that's why [Daniel] Nava is taking ground balls at first base. I understand all that coming into it. It's not that big of a surprise. I'll just do what I can and see if I fit, and that's all I can do."
Carp showed promise as a rookie in 2011, hitting .276 with 17 doubles, 12 homers, 46 RBIs and a .791 OPS in 79 games.
"I personally have seen a very good approach at the plate -- a guy that doesn't seem to be overexposed with one certain type of pitch thrown against him," said Farrell. "That's just been the firsthand view of him. The versatility to first base and left field, and by all accounts from across the field, he's been a hard-nosed player."
To make room for Carp on the roster, Ryan Kalish, who is recovering from right shoulder surgery, was moved to the 60-day disabled list. The 26-year-old Carp is out of Minor League options.
By contrast, the Red Sox would have to create a spot on the 40-man roster for Overbay if he makes the team.
"I haven't even thought about that really," Overbay said. "I don't want to sit here and say that works out [in his favor], because he's got to come in here and prove it, too."
In the coming days, Overbay will try to regain comfort in the outfield, where he played regularly before turning pro.
"That's part of it," Overbay said. "I think the biggest thing is if that gives me a better chance of making this team, then I'm all for it."
In 608 Major League plate appearances, Carp is a .255 hitter with 18 homers, 71 RBIs and a .740 OPS.