Hawks guard Trae Young takes a shot while Celtics center Robert Williams III tries to block it during Atlanta’s 130-122 win in Game 3 of their first-round series on Friday in Atlanta. Brynn Anderson/Associated Press

The signs were there early on Friday night that the Celtics’ defense was not going to be up to par in a Game 3 loss against the Atlanta Hawks. Boston hit a playoff franchise-record nine 3-pointers in the first quarter and still somehow led by only four points to start the second quarter.

Boston showed minimal resistance early, as the Hawks punished them in the paint. The wheels came off in the second quarter as Atlanta erupted for 41 points amid a flurry of points from its bench. When the damage was done, the Hawks had scored a playoff franchise-record 74 points in the first half, ensuring the Celtics would be playing catch up for the remainder of the night.

The Celtics tightened things up a bit in the second half, allowing 56 points, but failed to get critical stops late in a 130-122 loss. Boston allowed 127.2 points per 100 possessions – their fourth-worst defensive performance of the year and a troubling number against a .500 squad for a team trying to win a championship.

Last season, the Celtics didn’t play that poorly defensively in a single game all year, and their worst defensive performance in the playoffs was a 118-107 loss to Miami in Game 1 of the Eastern Conference finals. There were understandable excuses for that dud last May. Boston was coming off a grueling seven-game series against the Bucks in the second round and was without Al Horford (COVID) and Marcus Smart (ankle), forcing Aaron Nesmith and Daniel Theis into action.

This was a far cry from that tough scenario. Instead, Boston was on a roll going into Atlanta, with two days off after two largely dominant performances against a Hawks squad that looked overmatched. But the Game 3 version of the Celtics looked like a team that wanted to win with its offense, and that opened the door for Atlanta to find its rhythm on its home floor.

“We let some of their role guys get hot,” Celtics Coach Joe Mazzulla said. “I thought that second quarter dictated the game, where (Bogdan) Bogdanovic and (Saddiq) Bey made a huge difference when Trae Young went out. I thought that gave them life, and I thought they played a complete game, so in a close game like that, you might want to focus on the end of the game, you want to focus on the runs that led to that, and I thought that second quarter did.”

The Hawks shot 56 percent from the field, piled up 23 second-chance points and got 44 points off the bench. They took advantage of a Celtics team that came out defensively with the intensity of a regular-season game early and was never able to fully recover. Boston may have been a top-three defense in the regular season, but it was prone to defensive duds like this one at times, and that’s a recipe for disaster in the postseason.

“We have to do a better job of putting more pressure on them, being more physical, being more aggressive than passive in those situations,” Celtics forward Grant Williams said. “Dejounte (Murray), Trae were really comfortable tonight just getting downhill, hitting floaters. They were all tough shots, but when you give a team 74 points in the first half, they are going to feel confident about themselves. For us, it’s just a matter of making sure we are coming out with great defensive urgency, and the same thing with the defensive glass – we have to protect our shots and make sure they don’t get any second chances against us.”

The Celtics should still be able to take care of business in this series, but they’ve given life to an inconsistent Atlanta squad that has some talent. With potentially tall tasks awaiting them in the next two rounds of the East playoffs, a short and sweet series would have been attainable with an acceptable defensive performance in Game 3. Instead, the pressure is on to turn up the intensity in Game 4 and prevent Atlanta from making this a series.