Middlebrooks has hit in eight straight games in Pawtucket, batting .333 (11-for-33) in that span, with two home runs and a double.
He was demoted to Pawtucket on June 25 after batting just .192 in his first 53 games.
To make room for Middlebrooks on the 25-man roster, the Sox placed third baseman Brandon Snyder on the disabled list (retroactive to Aug. 8) with a right elbow injury. In another move, they activated LHP Franklin Morales off the DL and optioned RHP Pedro Beato to Pawtucket.
Middlebrooks' promotion does not preclude the possibility of highly touted prospect Xander Bogaerts also being called up in the coming weeks. Bogaerts could be used the way Jose Iglesias was, in a rotating system with shortstop Stephen Drew and occasionally filling in at third. Drew has been one of Boston's hottest hitters of late, batting .432 (16-for-37) in a 10-game hitting streak with two home runs and eight walks.
The Red Sox are 6-4 since trading Iglesias to the Detroit Tigers as part of a three-way deal in which they acquired starting pitcher Jake Peavy from the Chicago White Sox. Manager John Farrell has been employing a platoon of Brock Holt and Snyder since. Holt is batting .103 (3-for-28) while Snyder is batting .200 (2-for-10). The two have combined for no home runs and three RBIs, all driven in by Holt.
The Red Sox have gotten very little offensive production out of third base for the better part of a month. Iglesias batted just .167 (11-for-66) in his last 19 games for the Sox, his average plunging from .403 on July 6 to .330 at the time he was traded. All 11 of his hits were singles, and he drove in seven runs. He batted just .208 (5-for-24) in his first seven games for the Tigers.
In the 29 games since Iglesias went into his swoon, he, Holt and Snyder have combined to bat .181 (26-for-144) with one home run and 18 RBIs.
The position has been a trouble spot since the early weeks of the season. The Sox rank 26th in the majors in OPS at the position (.641), 28th in on-base average (.271) and 20th in slugging percentage (.370).
Middlebrooks, who was enjoying a terrific rookie season (.288 batting average, 15 home runs and 54 RBIs in 75 games) until his right wrist was fractured when struck by a pitch from Cleveland's Esmil Rogers on Aug. 10, came to camp this spring as the starting third baseman, a job he had wrested from Kevin Youkilis in 2012.
He got off to a fast start this season, hitting three home runs in a game in Toronto on April 7, the team's sixth game of the season. But he then plunged into the worst slump of his professional career over the next 14 games, batting just .093 (5-for-54) and striking out 20 times while walking once.
He also injured his ribs in a collision with catcher David Ross on May 7, and on May 24, Middlebrooks went on the disabled list with a lower-back strain, missing 16 games.
At the time of his demotion, Farrell said he explained to Middlebrooks that he should not expect an immediate recall. Of greatest concern to the club was an alarming strikeout-to-walk ratio: 60 K's, nine walks.
"Will will be getting regular at-bats," Farrell said. "For him to get back on track, he needs every-day at-bats.
"His skills haven't gone backward. He's still a very talented player. He needs consistent work that will allow him to replicate his swing. This isn't uncommon for a young player, to take a step back now for the bigger picture.
"He will be our every-day third baseman ... [but] this isn't going to be a numbers deal. It's not a matter of hitting .310 and coming back here."
Middlebrooks is returning after 45 games for the PawSox, in which he batted .268 with 10 home runs and 35 RBIs in 179 at-bats. He showed an improved selectivity at the plate, drawing 16 walks to 38 strikeouts. Middlebrooks acknowledged his frustration at being passed over while the Sox promoted Holt, Snyder and Jonathan Diaz ahead of him.
"Since I’ve been here I’ve seen a lot of my teammates get called up to Boston," he wrote in a diary for ESPNBoston.com. "How have I dealt with not getting the call? Well, of course I want it to be me. Who doesn’t want to get called up to the big leagues? It’s what you work for your whole life and play for, but I’ve had to put that frustration aside. I’ve realized when I’m frustrated or worried about that, I’m not focused on the right things to get me back to the big leagues. The first couple of times it happened, yes, I was frustrated. I wanted it to be me, of course. The last couple of times, I tried to look at the big picture. I know if I’m not focused on the right things, I’m not going to get back there.
"It’s not like Xander and I sit around talking about which one of us will get called up to play third base. We don’t discuss those things. He’s 20 years old. He’s not going to be 21 until October. He’s going to be a big-leaguer for a long time whether it’s third base, shortstop or wherever they put him he’s going to be a good player, that’s just his mentality. Like [Pawtucket manager Gary DiSarcina] said the other day, Xander would play on the moon. If we said we’re taking a trip to the moon to play baseball, he wouldn’t question you one time. He’d just say, 'All right, let’s go,' and be the first one on the bus. He’s just a kid, that’s all he is. He’s a kid with an extraordinary ability to play baseball."
Middlebrooks also indicated his back issue had not been fully resolved.
"I just want to be the player that everyone has seen," he wrote. "When I can get my body back to normal, I feel like everything will fall into place. It’s not an excuse because there have been plenty of other factors, like my approach at the plate, that snowballed on me. I just want to get back and help us win a World Series."
Middlebrooks, who was still en route when the clubhouse opened, was scheduled to meet with reporters after batting practice Saturday. He was listed as hitting ninth in the Sox lineup against Royals right-hander Jeremy Guthrie.