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On Sunday, in a 114-94 thumping of the Miami Heat, the Boston Celtics kicked off their quest to end a 16-year NBA championship drought with stellar defense, a red-hot game from deep and the sort of beat-you-from-anywhere-on-the-roster depth that can confound even teams as relentless as Miami.

It was a fabulous beginning. 

And -- no excuses here -- they sure better keep it going, on Wednesday night in Game 2 and throughout the remainder of the NBA's postseason.

That's the crux of the task in front of the Celtics. They can win it all, and in many ways, they must. The next two months lead to glory or gasps, confetti or consternation, a collective sigh of victorious relief or the possibility of real, and maybe lasting, damage.

This is a must-win season in Boston. And all the tools and traps are at their disposal.

The Celtics are, by any measurable standard, the game's best team: They have the league's best offense. They have its third-best defense. It would stand to reason, then, that they have the NBA's best net rating -- and they do -- but it's more than that. They have the third-best net rating in NBA history. The Celtics roster could not be deeper, particularly with the offseason additions of Kristaps Porzingis and Jrue Holiday.

The team's path, too, seems perfectly aligned -- just the kind of reward befitting a 64-win team and the No. 1 overall seed in the playoffs, East or West. This Heat team may be tough, but there's a toothlessness there, too, given the fact Jimmy Butler will miss the series with a sprained MCL. The Knicks, Embiid-is-back-Sixers and Bucks are on the other side of the bracket.

The road is open before them.

Winning championships rarely comes easy, just as regular-season excellence offers no sure guarantee. But this Celtics team -- so improved from the squad that two years ago lost in the NBA Finals to the Golden State Warriors, and lost last year in Game 7 of the Eastern Conference Finals on its home floor -- has no more excuses.

Yet worries remain. As does real, and perhaps impactful, pressure.

It was not quite a year ago, after that debacle against the Heat -- the Celtics had fallen behind 3-0 in that series before charging back and then losing that Game 7 in Boston -- that coach Joe Mazulla's seat grew very hot indeed.

He has returned this season with a vengeance. But winning in the playoffs is another animal altogether, and the only true gauge Celtics fans, and perhaps the Celtics brass, will turn to in assessing his success this time around will be the chase to win 16 postseason games.

Beyond the coach, there's also the Jayson Tatum question.

He is their bona fide star, an MVP-level scorer who's gone through enough postseason wars to have hopefully learned whatever playoff lessons one needs for greatness. Perhaps, like Nikola Jokic last season, Tatum is one marvelous run away from flipping the narrative surrounding him entirely.

But, at least so far, he has been unlike Jokic in his ability to be great in moments of real pressure -- a glaring, worrisome truth for any team chasing a championship.

The fact remains that Tatum can be quite unreliable -- read: often bad -- in the clutch. This is not a hot take, and it's more than some poor outings in the 2022 NBA Finals or last year's Eastern Conference Finals. The data is clear, and the sample size is large. 

This is not breaking news, but worth repeating: Teams need star players to play like stars in tight playoff situations in order to go where they want to go. Think Jordan. Think Kobe. Think LeBron. Think Jokic.

Hard, so far, to think at all about Tatum, at least in that context. It's also hard to believe that the Celtics will not play close or stressful games this postseason. Playoff domination happens, but it rarely happens without pressure. 

For the NBA, those pressure moments, clutch time, is defined as the final five minutes of a game within five points or closer. And by that definition, this season's Celtics are awesome: 21-12 in those situations and fourth in net rating at +15.4.

Fine. Great. Way to go.

But hold on.

The Celtics reliability in close games drops significantly when you ramp up the, no pun intended, heat. Look at games over the final five minutes that are within three points or fewer and the Celtics start playing like the San Antonio Spurs, Atlanta Hawks and Toronto Raptors.

In those closer, pressure-packed games the Celtics net rating drops all the way to 22nd, at -7.4, sitting right there with those teams that missed the playoffs.

Perhaps the Celtics are so good that, like the championship 2017 Golden State Warriors team that went 16-1 in the playoffs, they'll simply dominate so thoroughly that pressure moments won't really matter. Though even that Warriors team had to play a couple of close games on the way to winning it all, they largely won with ease.

More likely, Boston will, at some point, be tested. 

And when that test comes, some pressure-packed truths will be revealed with such a moment: That Tatum, poor under pressure stretching back years, will need to step up and reverse that fact. That Boston losing is brutally unacceptable, a weight heavier than we often give it credit for, especially with a team so dominant in the regular season. And that after several close calls, defeat this time around might start to feel like the kind of pattern that is building only toward disappointment rather than redemption.

The Boston Celtics are extraordinary. But they are not anointed to greatness. They have to earn that themselves. And their history, their star's past shortcomings, and the very real pressure clinging to their present-day, not-yet-set greatness means any slipup or setback would tell us whether they truly are this marvelous force we believe them to be.

Looking for more NBA coverage? John Gonzalez, Bill Reiter, Ashley Nicole Moss and special guests dive deep into the league's biggest storylines daily on the Beyond the Arc podcast.