While Youkilis started 349 games at the hot corner since his debut with Boston in 2004, the club is confident Middlebrooks can be their everyday third baseman moving forward.
The 23-year-old rookie is hitting .326 with nine homers and 34 RBIs in his first 41 Major League games since being recalled from Triple-A on May 2. That's the most RBIs by a Boston player to start a career since Walt Dropo drove in 37 in his first 41 games from 1949-50.
"Middlebrooks needs to be in the lineup, that's pretty clear," said general manager Ben Cherington.
Though the Red Sox identified Middlebrooks as their guy, he's trying not to look too far ahead.
"I'm approaching every day like I do every other day," Middlebrooks said.
For several weeks, manager Bobby Valentine juggled the rookie and veteran at third base. Middlebrooks' youth, potential and recent production eventually won out in the end, trumping Youkilis' track record and status as one of the team's most beloved players.
In fact, Middlebrooks' ability to maintain his production as he bounced in and out of the lineup this month helped convince the Red Sox he was their man moving ahead.
"He's been a pretty consistent performer since he was called up and I think the thing that ultimately tipped the scales is when he went through a tiny stretch there where he struggled a little bit in some at-bats and was in and out of the lineup a little bit and he really righted himself pretty quickly coming off that stretch," Cherington said. "That gave us some comfort that this guy is ready to make the kind of adjustments that big league players need to make. He'll make adjustments again down the road. It's not going to be smooth sailing like it is for any player. He's a talented kid, very confident, certainly has proven he belongs here and has helped us win games all ready and we're confident he'll continue to do that."
Middlebrooks has certainly helped Boston win during the first six games of the current nine-game homestand, going 10-for-16 with three homers, three double and 10 RBIs.
He showed signs of being an impact player from the moment he put on a Red Sox uniform with nine RBIs in his first four games. Middlebrooks hasn't slowed down since.
Still, Boston's confidence in the young Texan goes beyond what he's done on the baseball diamond.
"Aside from the performance that everyone sees, I think the fact that he's been in and out of the lineup some and is out a day or two and comes back and still has good at-bats, has made most of the plays defensively, fits into the clubhouse well, he's a confident guy," Cherington said. "We just feel like he should be our third baseman right now. He just needs to be himself. Like every good big league player, there will be tough days, but he's earned the right to be our third baseman and that's how we'll go."
Of course, it's not like the Red Sox planned on their top prospect to emerge as one of their biggest offensive weapons. Not this year, anyways.
"It's fair to say that we thought this would probably be his year in Triple-A, or at least most of the year, and things change. That's baseball," Cherington said. "Sometimes opportunities open up. Sometimes guys just speed the clock up because of what they do, and this was a combination of both. At the end of Spring Training we talked a lot with Bobby and myself and the staff about the guys in camp that weren't going to be on the team to start the season, and he was one guy that looked like a Major Leaguer in Spring Training. Even putting the Spring Training performance aside, he just handled everything really well. He looked like he belonged and looked like he knew he belonged."
Once Middlebrooks got his chance to be in the lineup everyday when Youkilis went on the disabled list with a lower back strain at the beginning of May, the rookie instantly provided a boost to the offense.
"We were confident coming out of Spring Training that if there was an opportunity, an injury or something, that he could come up and help, and that's what happened and he forced his way into the lineup with how he did," said Cherington, who is in his first year as Boston's GM.
And while Middlebrooks is the last man standing in the battle for third base, he's thankful for Youkilis' advice along the way.
"Words can't explain it," Middlebrooks said. "He's taken me under his wing and shown me the way and really made me comfortable."
In exchange for Youkilis and cash considerations, the Red Sox acquired utility man Brent Lillibridge and pitcher Zach Stewart from the White Sox.
"We'll get Lillibridge here, hopefully tomorrow, and he'll join the active roster," Cherington said. "Stewart will go to Triple-A and join the rotation. We don't know exactly what day he'll slot in, but we'll get him to Pawtucket and get him going."
Lillibridge, 28, was 11-for-63 (.175) in 49 games with Chicago this season. He split time at first base, third base, left field and center field. Lillibridge set a career-high with 13 homers for the White Sox last season.
Stewart, 25, made 18 appearances with Chicago this year before he was optioned to Triple-A Charlotte on June 19. With the White Sox, he was 1-2 with a 6.00 ERA and 16 strikeouts over 30 innings.
"These are two guys that we had focused on," Cherington said. "Lillibridge coming back was a fit that made sense probably for both sides. He helps us and gives us some protection at a lot of different positions and adds some versatility to our roster. With Youkilis going there, he probably wasn't going to get as much opportunity there. And then Stewart was a guy that we've liked for a while and were focused on. Ultimately, when they agreed to include him in the deal, that kind of pushed them to the forefront."
Lillibridge does not have any options remaining while Stewart has two.
The deal didn't center on those two players, however, this was all about Middlebrooks. The Red Sox believe he can develop into an All-Star, much like Youkilis did.
Youkilis is gone, but Will Middlebrooks is here to stay.
Austin Laymance is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.