ATLANTA — The momentum generated from a two-game winning streak, two easy victories highlighted by a stifling defense and 3-point barrages, was over just that quickly.
Once the Celtics faced adversity against a hot opponent, they folded again down the stretch. After battling to slice a 16-point deficit to 1 with under 10 minutes left Friday night, the Celtics lost all control with poor offense, costly turnovers, and shoddy defense in a 108-92 loss to the Atlanta Hawks at State Farm Arena.
The Celtics trailed just 85-84 after a Jayson Tatum jumper with 9:42 left and then scored 2 points over the next 7:05 to waste a chance at a third consecutive victory.
The Celtics missed 12 of their first 16 shots in the fourth quarter as the Hawks went on a 17-2 run to push Boston back to .500 (25-25).
Tatum, coming off 16 made 3-pointers in the past two games, was 2 of 8 from beyond the arc while Jaylen Brown (26 points) was 2 of 9. They combined for 12 turnovers as the Celtics shot 34.9 percent and were just 7 of 36 from the 3-point line.
Brown tied his season high with seven turnovers, including several strips of his dribble by Atlanta defenders.
“We failed to get [defensive] stops, turned the ball over too much,” Brown said. “We didn’t deserve to win that game. We played well in stretches, but I turned the ball over too much. We turned the ball over too much and that’s what cost us the game.”
The Celtics were 5-for-20 shooting in the final period, as their fourth-quarter miseries returned in what was a crucial game against a conference foe.
Atlanta, which made a spirited run to the Eastern Conference Finals last season but started 17-25, has now won six consecutive games. Trae Young and John Collins each scored 21 points Friday, but Bogdan Bogdanovic’s 19 points off the bench was more impactful during Atlanta’s big run.
Tatum, Brown, and Dennis Schröder each tried tying the game or giving the Celtics the lead with contested 3-pointers, all of them missed. The Hawks then took advantage of Celtics’ misses, sped up the pace, and pieced together that game-deciding run.
Tatum said he understood the perception he should have passed up those lower-percentage threes for drives to the basket.
“Those are the ones where if you make it, everybody clapping and [expletive],” Tatum said. “And when you miss it, you’re like, ‘I probably should have penetrated.’ As a basketball player, you kind of go with your instincts and figure the rest out later.”
The Celtics are now 21st in the NBA in fourth-quarter scoring, 25th in fourth-quarter field goal percentage, and 27th in fourth-quarter 3-point percentage.
“I guess you can say execution offensively hasn’t been great, really all season,” Brown said. “At times, when he hit those moments of adversity in the fourth quarter we tend to show what we’ve been in those moments. And we haven’t been very good in the fourth quarter and that translates from everything, execution from top to bottom.
“It just hasn’t been great this year, especially in those moments. We’ve lost too many games on the line.
The 62-47 halftime deficit was a byproduct of a 10-0 Hawks run to end the first half, and the Celtics could not allow the margin to get any larger in the third. They played with more pace and execution in but the Hawks maintained their lead because of Collins, who created a mismatch with any Celtic on the floor.
He scored four of Atlanta’s first five baskets in the third on an array of jumpers and short hooks. The Celtics countered with a pair of threes from Marcus Smart and then 10 combined points from Brown and Tatum, who passed on launching 3-pointers and dove into the paint.
The Celtics’ defense improved, challenging every shot as the Hawks began missing the contested ones they made in the first half. Tatum hit his second 3-pointer of the period to slice the deficit to 74-71, and the Celtics then avoided their typical late-quarter breakdown.
Brown ended the period with an acrobatic layup and then Josh Richardson took a brilliant pass from Schröder for a backdoor layup to cut the Atlanta lead to 80-77 after the third period after trailing by as many as 16.
The Celtics talked at morning shootaround about capitalizing on their previous two wins, which were by a combined 82 points. Tatum addressed the team and stressed staying focused to his teammates and starting Friday’s matchup strong.
The problem wasn’t the start. It was the finish to each quarter, which was awful in the first two periods for Boston. The Celtics were outscored 12-2 in the final 2:44 of the first period, and trailed, 32-20.
They matched that futility in the second by being outscored 10-0 in the final 2:20 and trailing by 15.
The Celtics outscored the Hawks, 45-40, in those other minutes, a testament to their maddening inconsistency.
Atlanta finished with 11 blocked shots, three of those on Tatum shots.
“This isn’t what we worked hard for or our fans are used to,” Tatum said. “Understanding that, we can feel pretty good about how we played the last two games but we didn’t accomplish anything. I wanted everybody to stay locked in. Obviously we didn’t do that for 48 minutes tonight. But I’m excited about [Saturday in New Orleans], you get a chance to redeem yourself and forget about this one.”
Gary Washburn is a Globe columnist. He can be reached at firstname.lastname@example.org. Follow him on Twitter @GwashburnGlobe.