DETROIT — Even arriving in the big league clubhouse didn’t totally made it sink in for Nick Castellanos that he was finally in the show.

Maybe it was the lack of sleep.

“Well, I found out, and then all the phone calls, and then being so excited, to reality sinking in that I’m not going to Columbus. I’ve got a 1:00 game here, and then an 11-day road trip to Boston and Kansas City and Chicago, after that. Then I realized ‘I gotta pack.’ Not only pack, but get my nice clothes out,” the 21-year-old third baseman-turned-outfielder said Sunday morning, after arriving at Comerica Park, having packed far more extensively than he would have in the minors.

“Minor league luggage involves a small duffle bag.”

[To hear audio of Castellanos' interview, CLICK HERE.]

Maybe for Castellanos — who was one of three September call-ups for the Detroit Tigers on Sunday, along with infielder Danny Worth and reliever Evan Reed — it will sink in when he goes to Fenway Park on Monday.

He and Avisail Garcia showed up in Boston to watch the Tigers play at the end of June last year, on an off day from their Double-A schedule, the unannounced arrival of two of the team’s top prospects creating a buzz that one or the other — or both — were being called up. Neither were at that point, although Garcia eventually was a late-season addition to the team and made the playoff roster, before being traded this season.

“It’s going to feel that much better going there for real this time,” admitted Castellanos, the team’s top minor league prospect, and top draft pick in 2010, as a high school player.

“I’m extremely fortunate to be able, first of all to be called up, and second of all to be called up in a situation like this, where we’re playing for something.

“I’m just going to take everything in, learn as much as I can, and enjoy the ride. It’s going to be a lot of fun.”

The Tigers already promoted infielder Hernan Perez and reliever Phil Coke on Saturday, and will add reliever Luke Putkonen Monday, then catcher Bryan Holaday and pitchers Jeremy Bonderman and Jose Alvarez on Tuesday.

At the moment, of those nine, only Perez and Coke are automatically eligible for the playoff roster, which had to be set by midnight Saturday. But any of the other seven could be, since the Tigers have two players on the disabled list — Luis Marte and Octavio Dotel — whose spots can be used to substitute a latecomer into playoff eligibility.

Ranked by both Baseball America and MLB.com as the 21st-best prospect in all the minor leagues before 2013 started, it was not a given Castellanos would be with the Tigers when it ended.

He acknowledged at the start of the Triple-A campaign that he’d always had an adjustment period to start his time at every level so far in the minors.

That was no different this year at Toledo, where he hit .276 with 18 home runs and 76 RBI. He surged in June, hitting .361 for the month, then struggled through July, posting a .212 average, before rebounding in August.

“At Triple-A, it was still an ongoing adjustment. Pitchers are smarter. You can’t take breaks. Everybody has great stuff. That’s why ... I’m not hitting .300 there,” he said. “That’s credit to the day-in, day-out great pitching we saw. You can’t take breaks. Everybody’s bullpen throws hard, they all — all starters — throw more than two pitches for strikes. So you have to learn. It’s constant adjustments. Catchers, if they you look a certain way in the batter’s box the first at-bat or so, they’ll stick with that same way (of pitching you), until you show them that you can make an adjustment.”

There’s also the fact that he’s just over a year and a half removed from being asked to make the switch from third base to the outfield, because his path to the big leagues was blocked by some guy named Miguel Cabrera.

“I felt like the third baseman we had in Detroit wasn’t going to allow me to play here anytime soon, so I viewed it as a very good thing,” Castellanos said. “Because I’m moving to the outfield, they see me here in the future. I could’ve hit .900 with 100, and I still wasn’t going to play third base for Detroit.”

So what has Castellanos improved upon through this season?

“Everything. When I was introduced to the outfield (last year), it wasn’t like I was reintroduced. I’d never played there before — ever. Not even in T-ball. I was new to everything. I was new to reads off the bat, I was new to line drives that are going to stay true, and line drives that have top-spin down. I was pretty rough with having wall awareness. ... Everything has gotten tremendously better, just from having experience and time out there. Seeing things that you can’t replicate in practice. Everything from balls in the sun, to line drives and night that go into the lights, and you’re going to have to stick with them,” he said.

“The throwing people out, knowing when you can air it out, knowing when you need to hit the cutoff man. Gene Roof (the organization’s minor league outfield/baserunning coordinator) has done an unbelievable job with me, and without him, I wouldn’t be in this locker room.”

Despite the desire to eventually be here in Detroit, Castellanos knew better than to sit around thinking about it too much. He wouldn’t have been all that disappointed if he had not gotten the call, considering he has a young infant son.

“It’s always there, but at the same time, you don’t want to just think about it over and over again, because I still had a season to play down in Toledo. So I just took it day by day. ... One way or another, I was going to see my son, so I’d be happy,” he said, noting that he was going to get to see his son on Sunday.

“He’s going to be here today.”