By Matthew Geagan, CBS Boston

BOSTON (CBS) — The Celtics are 1-2 on the young season and over the first three games, the team has provided plenty of ammo for its doubters.

Defensive issues? Check. Slow starts and blown leads in the second half? Check. Bad shot selection at the end of games by their budding young star? Check.

It is certainly worrisome that some of Boston’s issues from last postseason have followed the team home from the Orlando bubble. But those issues rearing their ugly head has led to some rather rash proclamations about the team, just three games into the season. Despite the fact that we all knew coming into the season that things would be a little tough without Kemba Walker in the lineup, and that the regular season was going to be a 72-game grind, the Celtics are already being written off in some sections of the fandom. It’s kind of wild.

Then again, the Celtics have been pretty wild over three games, making it tough to pin down where the team is at the moment. But at 1-2, they’re kind of right where we thought they would be — a team that has a lot of work to do throughout the season.

It’s been a packed first week of the season for Boston. The Celtics beat a title contender on their final shot on opening night, only to lose to another title contender a few nights later in blowout fashion. The team figures to fall somewhere in the middle of those two outcomes.

Then came Sunday’s game in Indiana. The Pacers are a pretty good basketball team as well, the kind that will likely give the Celtics fits throughout the year. (There will be a lot of them.) The Celtics should beat them on most nights, but we all know that doesn’t always happen. Being a middling team in the East, the Celtics can’t afford too many of those missteps, not in a season with very little margin for error.

So of course the Celtics went out and lost Sunday’s game in frustrating fashion. After holding a six-point lead at halftime, the Celtics sleepwalked through the third period, allowing the Pacers to score 39 points in the frame. Boston still battled back, but its late-game execution cost them, whether it was Robert Williams biting on a fake on defense and leaving a wide open lane for the go-ahead hoop, or Jayson Tatum’s ill-advised attempt at hero ball at the buzzer.

The loss stung a bit. Again, the Celtics can’t afford too many of those kind of defeats this season if they want to remain near the top of the Eastern Conference.

But the sky isn’t falling just yet, and Tuesday night will be a much better measuring stick of what these Celtics truly are — or what they can become. Boston can cast some doubt into the doubter’s doubts with a much better showing in Tuesday’s rematch with the Pacers.

These mini-series throughout the 2020-21 season will provide a great way to see growth from one night to the next for the Celtics and other middling teams throughout the NBA. If the C’s continue to make the same mistakes they did Sunday night, then we’ve got ourselves a problem. And if they come out and absolutely roll in Indy, you can feel a little bit better about the progress of the team.

Tatum got lucky with his game-winning banker on opening night, and he tried to essentially pull off the same move Sunday (minus the assist from the backboard). He should probably know by now that holding onto the ball while the final seconds tick off the clock before jacking up a contested three isn’t his best end-of-game option, but Sunday’s outcome was a nice reminder for the 22-year–old. If Tatum and the Celtics find themselves in that situation again on Tuesday, one would hope he’s got some other move ready to go, or maybe, just maybe, the play goes through someone else.

It’s going to be a bumpy ride for the Celtics during the regular season. There will be triumphant wins, close calls that didn’t need to be close at all, and, likely, a bunch more frustrating losses along the way. These Celtics are certainly not going to light the win column on fire, especially with Walker out. And even Walker’s return is not a magic elixir that will cure all that ails the 2020-21 Boston Celtics.

But what we’ll be looking for is growth along the way, something that will be a lot clearer when the team plays the same opponent multiple times in just a few nights. These short series will make it obvious if the team is taking the right steps to get better, or if they’re heading in the wrong direction.