WALTHAM — The Celtics’ locker room was silent Friday night.
“Everybody was real mad,’’ Avery Bradley said. “Nobody was saying anything.’’
The Knicks had just embarrassed Boston on its own parquet in Game 3, setting up a possible sweep during Game 4 of their first-round playoff series Sunday at TD Garden.
The Celtics were well aware of the Knicks showboating near the end Friday — the laughing, the pointing, the trash-talking — when they led by double digits.
“That’s what got us so mad, so angry,’’ Bradley said.
And the Celtics were clearly still fuming a day later, when they gathered at their practice facility to watch the footage of their 90-76 loss.
“Yeah, but you can be angry all you want, but how are you going to channel that anger?’’ Jason Terry asked. “Are you going to fight among yourselves or are you going to come out and fight the opponent?’’
There’s no question which of those options the Celtics must choose if they want to extend their season at least one more game. But it’s still unclear how they’ll respond down three games to none, a deficit from which no NBA playoff team ever has recovered.
“They haven’t won anything yet,’’ Jeff Green said. “They’ve just won three games. The objective is to win four. So, we still have a chance to do that.’’
Green added, “What we have to do is treat this game like it’s the last game of everybody’s career.’’
But the Celtics will have to drastically turn around their play to even make Sunday’s game competitive.
They already know the issues: too many turnovers, too many wide-open missed shots, too many lapses on defense, too many breakdowns for a team that can’t afford breakdowns.
“We don’t have a big margin of error,’’ coach Doc Rivers said. “We knew that going into it, and unfortunately we’ve made errors.’’
Such as not scoring points, which, as you might imagine, is quite the hindrance if one were aiming to win a competitive athletic contest such as basketball.
Boston hasn’t broken 80 points in any of its three losses, marking only the second time in the shot clock era (1954-55 season) that an NBA team has won the first three games of a playoff series and held its opposition to fewer than 80 points in each loss, according to the Elias Sports Bureau.
The only other time that has happened was in 1997, when the Michael Jordan-led Chicago Bulls held Miami to fewer than 80 points in three straight playoff wins.
“Something’s gotta break,’’ Terry said. “I mean, you’re not going to continue to just score 70 points every game. That’s just crazy. I’ve played youth basketball, AAU, I mean, I’ve never scored this least amount of points.’’
The Celtics also have fueled the Knicks’ attack by giving the ball away: New York scored 26 points off 18 Celtics turnovers in Game 3, for instance.
“We’ve got to stop doing that because every time we turn the ball over for them it leads to a bucket for them,’’ Bradley said.
Pride also will be a factor. The Celtics haven’t exited from the first-round of the playoffs since 2005 and haven’t been swept since 2004 against Indiana.
Moreover, they sure don’t want to be swept against an Atlantic Division rival, one that the Celtics themselves swept out of the first round in 2011.
“Sometimes their pride is what gets in the way,’’ Rivers pointed out. “Every single guy wants to win. They want to win so bad, they become an individual.’’
Rivers believed that type of play — commonly known as “hero ball’’ — occurred in Game 3. For Game 4, the Celtics have to simply play team basketball.
“Because if you don’t, we’re going to lose,’’ Rivers said. “That’s pretty simple. Now, whether I’m successful at it is a whole different ball game. It’s really important.
“That may be the challenge for me [Sunday] more than anything, because we do have the Jason Terrys on our team that want to win so bad that they may go into a game like, ‘I’m going to win this game tomorrow!’ Yeah, but it better be ‘we’ are going to win this game. That’s important, but it’s hard.’’
For Rivers, the season’s end is potentially here — a time he always dreads.
‘‘I just like to be able to know when the end is, meaning you’re in Game 7 of the world championship,’’ he said. “Then you know you’re playing for the end. I hate when the end can come early. But I dread them all.’’
But the Celtics won’t head into Sunday with a smile on their faces. They are angry, no doubt.
“I mean, when you get your butt kicked like they’ve been doing to us the last week or so and you’re seeing the same team every day, you’re going to get tired of it. Or you’re going to lay down. I’m tired of it,’’ Terry said.
If the game turns ugly, there’s a question of whether these Celtics will pack it in, ending a season in which they’ve been written off largely since Rajon Rondo suffered a season-ending knee injury.
“That drove us from the beginning,’’ Bradley said of the doubts. “Nobody had us winning. A lot of people said that they would sweep us.’’
And now that very well could happen.
But for the Celtics, all that matters, in what could be the end, is themselves and the game.
“You have to focus on the single game,’’ Rivers said. “You can’t win four without winning one.’’