Celtics coach Doc Rivers went with Jared Sullinger in the starting lineup again on Thursday night, and while Rivers insists that he hasn't made up his mind about any of his lineups, especially the starters, it's becoming more and more clear that Sullinger is the right fit. That's not taking anything away from Brandon Bass, who has literally done nothing to warrant a "demotion" to the second team.

Starter/reserve are tricky designations in the NBA, particularly when it involves a 20-year-old rookie and a seven-year veteran who just recently signed a new 3-year contract. Just a guess, but that's one of the reasons why Rivers is being so deliberate with his plan. Another is that he really isn't sure yet, and a third is that he's using the preseason to gauge who can play where and with whom, so he can take advantage of a tremendously deep and versatile roster. That's not playing coy, that's being smart.

And yet, through six preseason games, Sullinger has stood out both for his on-court play -- 11 points, 7 rebounds, 56 percent shooting in 25 minutes -- and for his demeanor. His notoriously hard to impress veteran teammates have embraced him in a way that would seem impossible around these parts.

Have we forgotten that Rivers himself has been judged to be a coach who refuses to play rookies? The coach's reply when that charge is brought up is always the same: Give me a young guy who can play and see what happens. Sullinger can play.

Two quotes in particular stand out.

First from Kevin Garnett:

"Sully is a very attentive. I love his IQ and everything he’s gaining as far as respect and anything else he’s gaining these last few weeks, he’s earned."

And from Rajon Rondo:

"He’s probably the smartest rookie we’ve had since I’ve been here. He’s very intelligent. High basketball IQ and he’s very unselfish. He doesn’t need a play called for him. [Emphasis mine.] He’s been getting his points off the dirty work."

What Sullinger brings to the starting lineup is points and rebounds. More specifically, as Rondo pointed out, he can get points without running the offense through him to get a shot. Sullinger moves well without the ball and has the touch and feel to score inside off passes and cuts. That skill alone will make Rondo's drives to the basket far more dangerous. 

Bass brings his own set of strengths to the equation. He is one of the best outside-shooting big men in the game, and when he's on the court with Garnett that opens up the floor. That's extremely important because the C's relied almost exclusively on spacing and ball movement to create shots last season. When Garnett and Bass were on the floor together, the Celtics scored 105.8 points per 100 possessions, a huge jump from their otherwise anemic offensive production last season.

However, Bass' biggest weakness last season was scoring at the basket where he shot just 55 percent per HoopData, the lowest mark in the league among rotation-level power forwards. Additionally, Bass is not the rebounder that Sullinger is, especially on the offensive glass where the Celtics struggled to the point of absurdity last season.

During the preseason Bass has played well with the second group. If he comes into the game with Jason Terry and Jeff Green, he can run pick and pops and keep the floor spread for Green to drive to the basket or post-up. That has the makings of a very effective bench. There's also a chance that Bass and Sullinger can play together in some lineups. We saw that on Thursday night against the Nets when Brooklyn coach Avery Johnson brought in Andray Blatche and Reggie Evans.

The real question isn't who starts. Rather, it's the specific lineups. There are 96 minutes to be had every night for the Celtics' bigs and Garnett will get 30 of them. That leaves 66 or so to be spread among Sullinger, Bass, Green and the backup centers. Those 30 minutes with Garnett are the most precious commodity on the team and Rivers will want to maximize them to the fullest.

Bass is the very definition of a solid pro, and he's the kind of player you want on your team. Again, he's done nothing wrong this preseason, but Sullinger has a chance to be special. What's the best way for him to reach his potential? By playing him alongside Garnett whenever possible.

These are the kind of choices Rivers will have to make all season long and injuries and attrition will also help settle out roles. It's a process, not an end-game in mid-October. But from where it sits now, the rookie from Ohio State should get the call on opening night.