Celtics Lack Consistency, Mental Toughness in First Game Without Kevin Garnett It was suggested to coach Doc Rivers on Friday evening, shortly after his Celtics had squandered a seven-point fourth-quarter lead and lost at home to New Orleans, that his guys had struggled to find their new roles in the absence of Kevin Garnett.

Specifically, the issue was an ill-advised 3-point attempt from Glen Davis with 1:23 left in a close game. Perhaps with the Celtics down three points and in desperate need of a big shot, a trifecta from Big Baby wasn’t the best idea.

“That’s a very good observation,” Rivers responded sarcastically. “It doesn’t take a rocket scientist to see that.”

With 14 seconds left on the shot clock, still plenty of time left for the C’s to move the ball and look for a good shot, Davis took matters into his own hands and heaved up a 3 to tie the game. It barely hit rim before landing in the hands of Trevor Ariza, and from there, the Hornets began to pull away.

Davis shouldn’t even have been in position to take the fateful shot — it’s supposed to be Garnett’s job to play power forward in crunch time, but with KG sidelined by a calf injury, Davis stepped up.

The missed 3-pointer, bringing Davis to 3-for-16 from long range for his career, was the end of a sloppy performance from the Celtics’ sixth man, and a perfect microcosm of the team’s game overall. The energy and the effort were there, but silly mental mistakes doomed them.

Davis left the TD Garden in a hurry Friday, avoiding reporters and slamming the locker-room door on his way out. He was in no mood to comment on the gaffe, but he didn’t have to. Rivers said it all.

“I thought we had a little bit of hero ball,” the coach said. “There’s no doubt about that. And usually, you lose when you do that. So we lost.”

The Celtics managed to lose on Friday afternoon despite an 18-0 run in the second half that appeared to all but seal the deal. They were down 66-55 in the final minute of the third quarter, but a flurry of big shots from Ray Allen, Marquis Daniels and Jermaine O’Neal staked them to a 73-66 lead with 6:26 to play. The win was theirs for the taking, but they just couldn’t take it. Turnovers, bad shots and lazy defensive possessions did them in. The Hornets fought back with a 17-8 run to close out the victory.

“It was a game of ups and downs,” Paul Pierce said. “We just didn’t play consistent. When you see that type of flow — going up, down, up, down — it means we just didn’t play consistent basketball.”

The easy explanation? The Celtics played like a team that lacked its two best players, Garnett and Rajon Rondo. But it wasn’t that simple. Beyond just the points, assists and rebounds, what the C’s really lacked was the mental toughness they needed to close out a win. They rattled off the 18-0 run, they got complacent, and they gave the game away.

“When we do have stretches like that, Kevin is our guy,” O’Neal said. “No matter what he has going on, whether he’s on or he’s off, he’s the guy that during timeouts is emotionally uplifting the team.”

But for the next couple of weeks, Garnett isn’t walking through that door. Whether they like it or not, the Celtics will have to find a way to win without him. So far, they’re 0-2 since their floor leader went down in Detroit on Wednesday night, and something’s got to give.

“If we want to be a championship-caliber team, then we really can’t have excuses,” O’Neal said. “The conversation coming into this season was how deep we are. So do we say, now that Kevin’s out for a while and Rondo’s been out, that we should lose? No. We shouldn’t say that. All of us have been in this position, and we know what it takes to win. We’ve just got to do our jobs better. No excuses.”