Then, midway through the second quarter, Brooklyn found itself staring at a 28-point deficit and seemed well on its way to a fifth straight defeat.
The Nets, though, had other ideas.
"There was a point in that first quarter, early second quarter, where we looked at each other and said, 'We're not going out this way,' and it kind of brought us together," Nets forward Cam Johnson said.
It not only brought Brooklyn together -- it also served as a catalyst for a remarkable turn of events. The Nets managed to completely erase that deficit by the early part of the third quarter and never looked back. They came away with a 115-105 win over the formerly East-leading Celtics in front of a shell-shocked sellout crowd.
The Brooklyn victory was the largest comeback win of the season for any NBA team, according to ESPN Stats & Information, and tied the largest comeback by any team over the past 25 seasons.
It also snapped a 10-game losing streak for the Nets against the Celtics, including last season's playoffs.
"I think we took our foot off the gas," said Jaylen Brown, who led Boston with 35 points, "and [Brooklyn] just ramped up their pressure a little bit."
What was a celebratory mood in the opening minutes -- Boston led 37-15 after one quarter and 51-23 with 7:23 remaining in the second -- was replaced by dismay and several rounds of boos as Brooklyn went on a ridiculous 83-39 run over a 24-minute, 29-second span.
"We started off well," said Jayson Tatum, who had 22 points, 13 rebounds and 5 assists while going 10-for-23 from the field and 0-for-8 from 3 (the most 3s he's ever attempted in a game without making one). "Lost our composure a little bit as a group. They kept rolling. We didn't necessarily regain it. It just became tough to come back."
As Boston roared out of the gate, it appeared it was going to be an easy night for the Celtics (45-19), who are now two losses behind the Milwaukee Bucks for the top spot in the Eastern Conference. But even as the Celtics took that 37-15 lead after the first quarter, coach Joe Mazzulla was concerned with how the game was going -- in particular that Brooklyn was getting up more 3s than Boston early on.
"I was actually worried because we were scoring, but it wasn't because we were making shots," Mazzulla said. "It was because we were getting layups. And they are a very analytically sound team. And so I knew the tide was going to shift because they were going to continue to shoot 3s, and if we didn't play at a level of shooting 3s and getting offensive rebounds and taking care of the ball, that was going to cost us."
It was a similar feeling on Brooklyn's side, as the Nets felt if they could stop making mistakes that allowed the Celtics to get one easy bucket after another, there was more than enough time to make a game of things.
"It really does," Johnson said when asked if early leads -- because of the number of 3s taken in Friday's game -- may feel smaller than they once did. "Especially when you know you're just messing up a lot and that's the reason for it. In the NBA, leads aren't safe. Leads just aren't safe, you know? People go on runs. Sometimes shots go in, sometimes they don't.
"And so you've just got to stick to the script, keep your head down and keep working, and we had that effort across the board today and the result was a win."
That also happened, in part, because Mikal Bridges had another explosive scoring game for the Nets. Bridges finished with 38 points -- 32 of which came after the first quarter -- on 13-for-22 shooting, including 4-for-6 from 3-point range, to go along with 10 rebounds, 4 assists and a steal.
Bridges now has the two highest-scoring games of his career -- 45 points in a win over Miami last month, and the 38 he scored against Boston -- in his first eight games with the Nets, after playing 365 games over the first four-plus seasons of his NBA career with the Phoenix Suns.
"Just trying to be aggressive, man," Bridges said. "The whole thing is just to go out there and win, and I feel like if I get to some of my spots ... I feel like I can make [shots]."
In doing so, the Nets (35-28) -- now 2½ games ahead of the Heat for the sixth in the East -- stunned the Celtics, who also nearly blew a large lead in Wednesday's win over the Cleveland Cavaliers.
Mazzulla, in addition to saying his team "let its foot off the gas," also pointed out how the Nets dominated every statistical category -- from taking and making more 3s and free throws to getting more offensive rebounds to taking more shots -- as an example of how his team simply didn't do enough to win.
Now, he said, it's on the Celtics to do better in these situations moving forward.
"You have to be able to handle it," Mazzulla said. "You can't get comfortable. It's hard to say, it's really hard to do, but you try to work through situations like that so that you say, 'Oh, is it really preventable?'
"No, it's not. Every team has done it. And so, to me, the area of growth and the opportunity comes in making sure it doesn't happen again if we're in that situation again."