The Boston Celtics planned on ending their first-round series Tuesday night against the Atlanta Hawks with an emphatic win to take the series in five games. Then Trae Young happened.

Young buried a 30-foot jumper from deep with 1.8 seconds left to clinch the comeback for the Hawks. What a comeback it was.

The Celtics led by 13 points with six minutes left and by 12 with less than three minutes on the clock. It was a brutal collapse that now forces the Celtics to head back to Atlanta for Game 6 and delays a second-round series with the Philadelphia 76ers.

Celtics head coach Joe Mazzulla was frank when he spoke about Young's game-winning heave. Mazzulla was pleased with the way Jaylen Brown defended Young, but he felt the Hawks star was going to make something happen one way or another.

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“I thought J[aylen] B[rown] did a good job keeping him in front. [Marcus] Smart was on his way up to go double to try to make him pass it, and he made a big-time shot from deep,” Mazzulla said.

“Any time you get into a close game with these guys, hindsight is 20/20 every time,” Mazzulla said. “Because if you take away the 3, he gets in front of you, he stops short and he fouls you. Can shoot a floater. If you help up, he’s going to throw a lob or kick out.”

The Hawks closed out the game with a 37-point fourth quarter. The Celtics and Joe Mazzulla were left shaking their heads.