BALTIMORE – It’s decision day, and Will Middlebrooks is suppressing his curiosity.

“I try not to think about it,” Middlebrooks said of the uncertainty of whether he will be in the majors or the minors when the dust settles and Kevin Youkilis is activated. “I’m really not worried about it. Whatever happens happens, and I know it will be for the best for the team.”

In some respects, what the Red Sox decide to do with their roster is less significant than the fact that they have a choice. And that development reflects entirely on the performance of Middlebrooks, who once again demonstrated on Monday why he is such a highly regarded part of the Red Sox’ future and, in all likelihood, its present.

Middlebrooks has looked entirely comfortable during his big league tenure. He has, in the parlance of the industry, looked like he belongs both on the field and in the clubhouse.

His call-up has had three chapters. The first was his historic debut, in which he became the second player since 1900 to begin his career with extra-base games in each of his first five games. Then came the league’s adjustment, a nine-game stretch in which Middlebrooks went 6-for-36 (.167) while punching out 15 times.

But then, perhaps most significantly, came Middlebrooks’ rebuttal. While in Philadelphia, against a group of pitchers that included Cole Hamels and Cliff Lee, Middlebrooks rebounded. He was 4-for-11 in Philadelphia, then scalded the ball en route to a 3-for-5 night on Monday in Baltimore in the Red Sox’ 8-6 victory.

He was not in awe of his opponents or overwhelmed by his struggles. He instead felt both comfortable and determined.

“It’s cool [to face pitchers like Lee], but at the same time, I want to get the better end of it. I want to beat them. I want to hit a rocket into the gap,” said Middlebrooks. “I don’t want to strike out and just say, ‘Oh, that was Cliff Lee. He’s got nasty stuff.’ I feel like I belong here. I want to play here. And I want to get hits off of him.”

The idea that Middlebrooks could enter and then exit a slump was arguably more significant than his electrifying start. Baseball history is littered with the names of players who had a meteoric ascent and then almost immediately disappeared, never to be heard from again. The fact that Middlebrooks showed the ability to rebound so quickly from his first big league period of struggle is a key sign that he belongs to a different category of player.

“It was a little rough patch, but I got through it, got some knocks last series and felt good coming into this one,” said Middlebrooks. “That’s part of the game, is failure and digging yourself out of a hole. The thing is not to dig yourself too big of a hole, which is something I’ve learned to do the last few years. You’re going to have a week where you’re not seeing the ball well. We faced some really good pitching, too. I stay positive through it. When it’s good, it doesn’t last, either. It’s just a cycle and you’ve got to stay positive.”

Of course, the challenge of doing so was made more complex by the uncertainty about where he would ultimately play. As the rest of the baseball world spent the last few weeks debating the merits of what the Red Sox should do with Middlebrooks upon Youkilis’ return, about the only player who seemed unfazed was the rookie, and with good reason. The idea that the Youkilis/Middlebrooks situation represented an either/or scenario was turned on its head on Monday.

Youkilis wrapped up his minor league rehab assignment on Monday night, going 1-for-2 with a double and a pair of walks. After collecting four hits in 11 at-bats in Triple-A, he appears ready to slide back into a big league lineup, representing, according to manager Bobby Valentine, “just what the doctor ordered.”

The veteran’s return had been viewed by the club as an almost certain harbinger of a return to the minors by Middlebrooks until Monday, when an MRI revealed that Cody Ross suffered a fractured navicular bone in his left foot when he fouled a pitch off of his instep on Friday. Ross will land on the disabled list today, thus creating an opening on the roster and a need on the part of the Sox to accumulate as many talented right-handed hitters as possible on their roster.

And that, in turn, means that the Sox found themselves on Monday contemplating creative solutions, most prominently the idea of keeping Middlebrooks and Youkilis in the majors. In order to do so, the Sox would have Adrian Gonzalez play some right field in order to give all three players time on the field.

“We lost a good right-handed hitter today for a while so it’s hard to lose more right-handed hitters. [Keeping both Youkilis and Middlebrooks on the roster] is a consideration in light of that,” said Cherington. “We’re still talking about it. We’ll see how it would work. At a time like this, it’s important to slow things down and try to make decisions for the right reason. We want to do what’s best for the team, certainly, but also what’s best for the players.

“[Keeping both players in the majors and having Gonzalez play some right field] is something we’ve discussed and talked about what it would be like if we did. At a time when you have a lot of injuries at one spot, sometimes you might have to come up with solutions that you might not have thought of two months ago. We’re talking about all sorts of things.”

But it is the performance of Middlebrooks that has, in many respects, forced the conversation. In 18 games, he’s hitting .297 with a .325 OBP, .581 slugging mark, .906 OPS, five homers (tied with Dustin Pedroia for fifth on the team) and 16 RBI.

He is clearly a player whose development is not finished. He’s made some errors in the field that represent a lack of repetitions and experience. On Monday, he was thrown out trying to steal second, at a time when the red-hot Jarrod Saltalamacchia was at the plate.

But those mistakes, borne of aggressiveness and inexperience, are palatable for the team given everything else that he has done.

“He’ll learn from an aggressive mistake,” said Valentine. “I’m not taking his instincts away from him the way he’s playing.”

And he will succeed with that same aggressiveness. In fact, he is succeeding with it. Middlebrooks made a game-changing play on the bases, after all, bluffing towards the plate off of third base, at a time when the Sox trailed the Orioles 5-4 in the sixth inning, to force O’s starter Tommy Hunter into a game-tying balk.

“You wait another second and he’s already in his windup. You start another second early and he steps off. [Middlebrooks] went exactly as [Hunter] was in that no man’s land – oh, I should step off; no, I can’t – it was a veteran move,” said Valentine, before correcting himself. “A lot of guys think it’s a Little League move, actually. He’s the least removed from Little League. That’s how come he knew how to use it.”

Such jokes aside, Middlebrooks has looked like anything but a baby in the majors. And in that sense, his first 18 games have offered a noteworthy glimpse into just how far his career has come.

Back in Single-A Greenville in 2009, Middlebrooks’ manager Kevin Boles saw a player who lacked visible conviction in his abilities. Then 20, Middlebrooks was just starting to believe in his talent but he had nothing like the presence that he now exudes.

“[Boles] always said, ‘I’m trying to turn you into an animal. Right now, you’re just a meek little lamb,’” recounted Middlebrooks. “You’ve got to play like you’re the best player out there and you believe it. They’ve been driving that into me -- ‘You’re the best out there; you’re the best in the league’ -- and I started to believe it.”

Middlebrooks said that it was last year in Portland -- where Boles was once again his manager, having moved up the ladder with him to High-A Salem in 2010 and Portland in 2011 -- that he gained that sense of certainty in his abilities. The third baseman had a chance to take stock of how far he’s come during a recent phone conversation with Boles.

“The first thing he said was, ‘You’re not a meek little lamb any more.’ I said, ‘Well, you contributed to that,’” said Middlebrooks. “He was a huge part of my development.”

Many people contributed to the third baseman’s development, but ultimately, it is the 23-year-old who is responsible for having made his case to stay in the majors. He has played not as if he is in the big leagues on borrowed time but instead as someone whose career is getting ready to take flight.

“That was my plan, to come up here and make a statement that I can play here and hopefully stick around and help win some games,” said Middlebrooks.

Mission accomplished, which is why Middlebrooks may be staying around for a while.