Apr. 26—BOSTON — There’s bad losses, then there’s inexplicably putrid losses.

The Celtics 119-117 setback to the Atlanta Hawks in Tuesday’s opening round Game 5 falls into the latter category.

For three-and-a-half quarters Boston played well enough to win. They weren’t perfect, but they still held a double-digit advantage midway through the final frame in front of a raucous home crowd.

And then, Trae Young went to work. The streaky sharpshooter closed things out the same way he started it: by raining in a 30-foot triple with under two seconds to play to give the Hawks the lead for good.

Boston had a chance to tie or win it at the buzzer, but their first inbounds pass was knocked back out of bounds and with just 0.5 ticks remaining after that, Tatum’s last second heave from beyond the arc fell short.

“We just lost our poise a little bit down the stretch, didn’t execute and put ourselves in tough spots against a talented team,” said Celtics head coach Joe Mazzulla. “It never comes down to one play; in the second half we didn’t execute the way we normally do.”

Young finished the evening with a game-high 38 points and 13 assists. He took a whopping 33 shots, making 14 of them including five from distance.

But as good as Young was, this loss falls on the Celtics more than anything else. It was almost as if you could see the collapse coming — a haunting reality that Boston fans probably figured was in the past.

In crunch time, Boston got away from what they do best: moving the ball, playing with pace and energy and grinding on the defensive end.

Instead, the Celtics decided to go through the motions and bank on their talent to win out.

“You can control what you focus on and at the end of the day we have to play the level of basketball that we’re capable of playing,” said Mazzulla. “We have to be the aggressive team, the more physical team; nothing matters except our approach to the game.”

Jayson Tatum had a particularly rough night. He scored 19 points but shot just 8-for-22 from the field and a horrendous 1-for-11 from deep. Time and time again he settled for long jumpers despite never finding his rhythm from distance. He was also whistled for a technical foul with time winding down, allowing Young an extra free throw that ultimately put the Hawks in front.

Defensively, Al Horford — who is almost never to blame in losses like this — more than did his part. He blocked five shots and swiped a steal, locking down the paint against Atlanta’s bigs and driving guards.

But as a whole, Boston left plenty to be desired on that side of the court. The Hawks hit 19-of-41 shots from deep (46.3%), many of which were wide open.

Then there’s the coaching. As impressive as it’s been to watch Mazzulla lead this team all season, he made some questionable decisions Tuesday night.

Blake Griffin, for one, was inserted into the lineup for the first time this playoffs with just over 10 minutes to play in the game. To his credit, Griffin had played well in spotty minutes throughout the regular season. But dusting him off and throwing him into the fire in the fourth quarter of a potential seriesclinching game was a hard one to figure out.

Mazzulla also opted to take Sixth Man of the Year Malcolm Brogdon, who had played another efficient, mistake free game, out of the contest with seven minutes and change remaining and Boston still holding an eightpoint lead. Having Brogdon on the floor to direct traffic down the stretch seemed glaringly obvious, not to mention the fact that Derrick White, another key ball handler, was out of the lineup late, too.

It’s easy to go back and look at where the Celtics went wrong. Bottom line: they didn’t play winning basketball, and it cost them against a Hawks team playing with house money after their second best player, Dejounte Murray, was suspended for Tuesday’s game after making contact with an official last time out.

Now Boston has to travel back to Atlanta for a pivotal Game 6. And of more pressing concern, they give Embiid and his Sixers more time to rest and gear up for another potentially long series in Round 2.

The Celtics are only making things harder on themselves by allowing an inferior Hawks squad to stay alive. And now, it’s anyone’s series to take.

“Obviously it’s a tough loss but I’m confident that we’re gonna come back tomorrow and figure out what we need to work on and be ready again for Game 6,” said White, who finished with 18 points, five rebounds, four assists and a pair of blocks.

“We have a lot of guys in here that trust each other. We just have to lean on each other and get through this together. “