The Boston Celtics waved a huge red flag during their second-half collapse against the 10th-seeded, Trae Young-less Atlanta Hawks on Monday night, which Kendrick Perkins deems a considerable concern.

After leading the Hawks by as many as 30 points in the second quarter, and following a 44-point first quarter, the Celtics fell flat on their faces. Boston scored just 44 points in the second half, recorded zero assists in the fourth quarter and blew the franchise’s largest lead in the play-by-play era (since 1996-97) with 11 games remaining before the playoffs begin.

Perkins, however, isn’t giving the Celtics — who’ve already secured the No. 1 seed in the Eastern Conference — any leeway for crumbling miserably.

“When you look at this recipe and they continue to shoot threes, the ball continues to get staggered, and especially when they’re in close games this is a habit,” Perkins said Tuesday on ESPN’s “NBA Today.” “And teams are looking at them and saying, ‘You know what? If we do those things, we actually could beat them,’ and they do not fear the Boston Celtics.”

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In hopes of leaning toward their outside shooting, the Celtics shot an abysmal 1-for-15 (7%) in the second half, giving the Hawks plenty of wiggle room to swoop in and expose Boston’s still-existent vulnerability.

Celtics head coach Joe Mazzulla chalked the jarring performance, which ended Boston’s win streak at nine games, to a “good lesson” after the 120-118 loss — the worst the team has suffered this season. Although in the grand scheme of the regular season the loss impacts the Celtics in no way, shape or form, it’s still alarming that a healthy Jayson Tatum and Jaylen Brown can still fall content and mistreat an opportunity to abuse a weaker opponent.

This was the case in last season’s playoff run in which Boston allowed the Hawks to extend their first-round series to six games. Then the Celtics allowed a limping Joel Embiid-led (in Games 2-7) Philadelphia 76ers go to seven games, and lastly the No. 8 seed Miami Heat take a 3-0 lead in the conference finals before finishing Boston in Game 7.

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The Celtics have lost just 15 times this season and only a handful were concern-level defeats, but at the tail-end of the campaign is when Boston should be toying with teams like the Hawks. Instead, the Celtics were left scratching their heads while Jayson Tatum was bombarded with, ‘You’re not Kobe’ chants from Atlanta fans at State Farm Arena.

“We just took our foot off the gas and they just got confidence, and at that point, it’s tough to beat anybody when they got it rolling,” Brown said postgame, per NBC Sports Boston. “… We’ve had the right approach. Tonight wasn’t the best example of that. We kind of took our hands off the steering wheel a little bit. And no matter if we up 30 (points) or we down five, we gotta have the same approach and the same mindset.”

Boston can’t afford any learning lessons once the playoffs officially commence. Tatum, Brown and the Celtics have lived through that gut-wrenching script a handful of times already.

Featured image via Brett Davis/USA TODAY Sports Images