The Celtics have spent the last few weeks trying to convince the world they can beat the best teams in the NBA and be a serious postseason contender.

It might help their argument if they could beat the worst.

The Bobcats had lost their previous 10 games by an average of 21.5 points, no less. After last night they have now won three of their last 21, and two of those triumphs have been at the expense of your Boston Celtics. The latest was a 100-74 Shamrock shakedown before a largely green-clad crowd that left the building feeling blue.

“Tough night, man,” said Kevin Garnett. “Tough night.”

The C’s could brush away the 94-91 loss here a month ago to the fact they were exhausted after winning a triple-overtime game the night before. For this one, they chose to rest leading scorer Paul Pierce, but that doesn’t fully explain the mess that was their offense (27.6 percent shooting in the second half, 40.9 percent for the game).

It didn’t help that second-leading scorer Garnett followed up his 5-for-19 shooting in Oklahoma City on Sunday with a 2-for-10 performance against the now 14-50 Bobcats. Garnett had five points when he was yanked early in the fourth quarter as the Charlotte lead grew to 20.

And neither Pierce’s absence nor Garnett’s wayward shots are proper reason why Gerald Henderson went for a career-high 35 points or why the Cats, the worst defensive rebounding team in the league, busted the Bostonians on the boards, 48-29.

Pierce had the night off, and he had company.

Asked how much of this can be pinned on Pierce’s absence, coach Doc Rivers said, “Well, not all of it. I just thought we approached the game with the wrong mentality. I thought we were really cool tonight, and they were really hard. And then I thought everyone kind of thought that they were going to take up for Paul’s points instead of coming in the game with the right mentality.