By Matthew Geagan, CBS Boston

BOSTON (CBS) — The Celtics once again no-showed for their latest “biggest game of the year,” and are now facing a reality as an NBA play-in team.

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In falling to the Heat on Sunday, 130-124, the Celtics are now two games back of Miami for the six-seed in the Eastern Conference. With just four games remaining, including a rematch with the Heat down in Miami on Tuesday, the odds are slim that Boston will be able to leapfrog Miami in the standings.

If the standings don’t shuffle over the next seven days, the Celtics will have to play the Charlotte Hornets for the right to be the East’s seven-seed in the NBA play-in tournament. The winner of that game moves on to face the two-seed, which is currently occupied by the Brooklyn Nets. (Good luck with that.) The loser of that play-in game plays the winner of the other play-in game between the No. 9 and No. 10 seed, with the winner of that matchup taking home the eight-seed.

It’s a pretty terrible spot to be in for a team that had so much promise to start the season. But it’s where the Celtics find themselves after yet another disappointing defeat on Sunday, and they really have no one to blame but themselves.

There was no defensive resistance from the Celtics in the team’s biggest game of the year. If you just had some Deja Vu, it’s because we’ve said this countless times during the season.

“They outplayed us, obviously, in the first half. There’s no excuse for that,” head coach Brad Stevens said of Boston’s 79-53 hole at halftime. “Certainly anybody on the Celtics side, we’re all responsible for that. But first and foremost, I think that would fall on me and so we have to do a better job.”

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Boston made a surge in the second half, but like most comeback bids throughout the season, it was too little, too late. And if anything is clear about this team, it’s that they are not ready for the playoffs. Or the play-in. Basically, they aren’t ready for any game that carries any consequence.

They certainly weren’t ready for Sunday’s showdown with the Heat. A win would have given the Celtics some chance to avoid the play-in, drawing them even with Miami in the standings and giving them the head-to-head tie-breaker against the Heat. It wouldn’t have guaranteed the six-seed, but there would have been hope. That hope was extinguished pretty quickly when things tipped off on Sunday.

After falling behind in Chicago on Friday night, the Celtics fell behind on their home floor in a game with major playoff ramifications. Forget about the team flipping a switch for the playoffs — they can’t even find the darn thing in must-win games during the regular season.

“I don’t think that we’re necessarily good enough to just turn the switch on,” said Jayson Tatum. “Like ‘all right, let’s play.’ Certain games here and there we’ve done that and been able to win. Obviously today, we dug ourselves a hole. We gave ourselves a chance. We’re always going to do that.

“But I know that we can do better, do more, especially in the beginning of the games, just play with a little bit more toughness and play faster,” added Tatum.

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The players know they can do it, they just haven’t been doing it for a myriad of reasons. And now they face the reality that they’re going to have to play a game or two just to qualify for the playoffs. Based on what we’ve seen all season, there’s no guarantee they show up for those, either.