Aceves was sent down after a meeting with manager John Farrell, pitching coach Juan Nieves and general manager Ben Cherington in Farrell's office after Boston's 6-5 win over Oakland at Fenway Park.
Catcher Ryan Lavarnway, who is hitting .310 for Pawtucket, will take Aceves' roster spot, according to a team source.
The need for Lavarnway could stem from ongoing back issues for outfielder Shane Victorino, who was forced out of Wednesday's game. Lavarnway would give the Red Sox a right-handed bat and possible DH, particularly if the Red Sox need to play Daniel Nava and Jonny Gomes in the outfield. The team said a corresponding roster move will be made Thursday.
Aceves made three starts while John Lackey has been on the disabled list with a strained right biceps. Lackey is scheduled to throw a bullpen session Thursday, and if all goes well, he will start here Sunday against the Houston Astros.
The tenuous nature of Aceves' place on the Red Sox was reinforced during Farrell's pregame session with the media, in which the Boston manager reiterated that the club's tolerance for his erratic performances was growing short.
"I think the bottom line is just that, the bottom line," Farrell said. "You've got to perform to continue to get opportunities."
Aceves had gone five innings in each of his first two starts, throwing 106 pitches last week in Cleveland before home runs by Nick Swisher and Jason Giambi knocked him out in the sixth inning. His ability to come out of the bullpen and serve as an emergency starter is what gives him value to the Red Sox.
Then came Tuesday night, when, in ghastly weather conditions, Aceves pitched as badly as the weather, especially in a third inning in which he walked three batters, committed two balks, was late in covering first base and made a throwing error. The next inning, he gave up a home run to Seth Smith, even with a strong crosswind sweeping Fenway Park.
Through three starts, he has allowed 20 hits, 10 walks and four home runs in 13 1/3 innings with an 8.10 ERA.
After Tuesday night's game, Farrell spoke of a loss of "focus" while a clearly emotional Aceves, in a rambling back-and-forth with reporters, mentioned the weather, the hole dug by opposing pitcher Bartolo Colon and a small strike zone as factors in his performance. Aceves, who spoke in English but has made it clear he's not comfortable in his second language, took responsibility for covering the bag late and for making a bad throw. He also made a vague reference to Red Sox hitters not having success against Colon, which some construed as calling out his teammates.
Farrell said he didn't read it that way.
"I will say this: Setting elements aside, Bartolo was probably as sharp as any time this year," Farrell said. "When he's on, he can shut a team down. He came in here undefeated and remains that way. I don't know if in that context Alfredo was calling out his teammates. I don't believe he was.
"There was some frustration and some, I don't know how to describe it other than some indecision on his part inside that game. If that's how he chooses to describe it, I wouldn't put it on his teammates by any means."
Farrell said he met Wednesday morning with Aceves.
"I had a chance to meet with Alfredo today just to discuss last night, not a role going forward," Farrell said, "but it still comes down to you need to earn these opportunities, and there have been mixed results."
In addition to Lackey, the Red Sox have several pitchers on their way back to being activated. Joel Hanrahan threw a bullpen Wednesday afternoon and is slated to head to Pawtucket on Friday, barring any setbacks. Left-handed reliever Craig Breslow, who started Tuesday's game for Portland, is scheduled for back-to-back appearances in Pawtucket on Saturday and Sunday.
Left-hander Franklin Morales, meanwhile, remains a question mark and might have his rehab assignment stopped. He developed some soreness in his left pectoral muscle while pitching for Class A Greenville earlier this week, and was brought back to Boston to be re-evaluated and placed on a long-toss program. The Red Sox have not scheduled when he will make his next appearance.