Trae Young was out with right Achilles tendonitis. Bogdan Bogdanovic dropped out with right hamstring tendinopathy.

But the Atlanta Hawks had Onyeka Okongwu, and the big man was there when they needed him most and delivered a game-winner.

Boston had a few chances to get the win back, but had a turnover on an inbounds pass to Jayson Tatum, then Jaylen Brown missed a good look at midrange and the Hawks escaped with a win in Boston.

Dyson Daniels stepped up on both ends of the court and scored 28 to lead the Hawks, while veteran Larry Nance Jr. added 19 off the bench for Atlanta. Okongwu finished with 15 points.

Brown was on fire for much of the game, finishing with 37 for Boston, while Derrick White had 31 points, including seven 3-pointers.

The Celtics haven’t been sharp lately; they have enough talent to keep winning games even without Kristaps Porzingis (and Brown missed a handful of games, too), but they haven’t looked like themselves. Call it a mini-slump, a delayed championship hangover, or whatever you want, but this was a tough loss.

Atlanta is now 1-0 in Group C NBA Cup play. If Boston wants to advance from group play to the knockout round, it must beat Cleveland in a big match next Tuesday, win to finish 3-1 and to achieve a victory. a few blowouts there (point difference is a tiebreaker).

To do all that, the Celtics need to be sharper than they have been lately.