ATLANTA — Friday’s loss in Chicago was a humiliation. 

This one was a heartbreaker. 

The Nets fought back from a huge deficit to tie, only to watch Trae Young beat the buzzer — and them — with a clutch floater. 

The end result was a 129-127 gut-wrenching defeat to the Hawks that sent the sellout crowd of 16,983 at StateFarm Arena into delirium and the Nets to yet another tough defeat. 

It was Brooklyn’s fourth loss in five games since trading Kevin Durant. 

“Yeah, great challenge. It’s a part of basketball and you can’t feel sorry about yourself,” Jacque Vaughn said. “I’m not gonna give them excuses about this, spin a new group and this is only their fourth or fifth time playing together and the lack of practice and all that stuff. People, you can hold on to that. 

“Not going to give that to the group. What we have to do is continue to stay together and believe that we can get it done. That’s the mental hurdle for this group.” 

Brooklyn (34-26) was still stinging from a 44-point thrashing by the Bulls and were down 18 Sunday before rallying. It was a rally that came up just short. 

Dorian Finney-Smith’s 3-pointer pulled the Nets within 127-124 with 48.3 seconds left, and when they forced a Young miss — and Spencer Dinwiddie snatched the rebound — they had one final chance to tie. 

Cam Johnson (team-high 27 points) did his best to make it count. When Finney-Smith drove and Johnson’s defender peeled off, Finney-Smith hit Johnson wide open in the left corner for a game-tying 3 with 7.8 seconds left in regulation. But they couldn’t hold on to reach overtime, thanks to Young. 

The Nets left Mikal Bridges (24 points) on Young, and he played solid enough defense on the first move, a crossover. But when the Hawks star got Bridges in the air with a pump fake, Dinwiddie came over from behind to try to get a piece of the shot. But the 12-foot floater was good, just beating the buzzer. 

“I’ve just got to stay disciplined. I jumped, left my feet. But I’ve just got to stay disciplined,” Bridges said. 

“Oh man, honestly I thought I had it,” Dinwiddie said. “The only thing about it is you don’t want to be too aggressive and get called from a foul, because you definitely lose. Bang-bang, clock is running down. I thought Mikal had him at first. He had great defense on the first couple of moves. The pump-fake kind of [shook] Mikal, that’s why I peeled off of [Bogdan Bogdanovic] feeling like there wasn’t enough time to get the pass off and for him to fire it. 

“I thought I was going to block it. You’re going to swipe a little more tentatively because .5 on the clock, if you foul him and give him two free throws, he only had to make one. It’s Trae Young, and he’s going to make the free throws. … You’re not mad at the shot and Mikal played great defense. Trae Young’s a helluva player. You’d rather not be in that position.” 

Young finished with 34. 

John Collins — who returned from concussion protocol and a bad back — put the Nets in a pair of 18-point holes, the second at 57-39 with 5:36 left in the half. Through that point, Brooklyn was allowing 57 percent shooting and 9 of 15 from 3. 

After going behind by 18, Brooklyn tightened the vise and held the Hawks to just 4 of 19 shooting in an extended 35-14 run that spanned intermission. A Nic Claxton layup capped the run and pushed it to 74-71. 

A Cam Thomas free throw made it 92-89 with 1:10 left in the third, but they coughed up an 8-2 lead to trail by three going into the fourth. It swelled to 127-119 on a Young free throw with 1:17 to play in regulation. 

A Dinwiddie dunk and Finney-Smith 3 got them within three with 48.3 seconds left. Johnson’s 3 pulled them level, but Young untied it. 

“We got one-on-one coverage a little bit,” Vaughn said. “We had some shell defense around him. Give him credit for the shot that he made with a contest from behind by Spencer, so good shot. Give him credit.”