Celtics can't stop Mavs, skid

BOSTON -- The 1986 Bears? The Celtics' defense has looked more like that of the 2009 Patriots with the way Boston has wilted in the second half while dropping three straight at home.

The Celtics held a nine-point advantage coming out of halftime Monday night and led by as many as 12 in the third quarter before the wheels came off. Dallas scored 15 of the final 18 points of the quarter, which helped the Mavericks emerge with a 99-90 triumph at TD Garden.

After shooting 46.9 percent (15-of-32) in the first half, the Mavericks finished at 57.4 percent (39-of-68), blistering the field at 66.7 percent (24-of-36) after intermission.

That included a stretch spanning the third and fourth quarters during which the Mavs connected on 12 of 13 shots and outscored the Celtics 33-10 to open their largest lead, 93-75, with 6:56 to play.

"We've got to understand, we are a defensive team first," said Celtics captain Paul Pierce. "Regardless of who we put on the floor, at the end of the night, regardless of if we shoot the ball well or not, we are a defensive team. And that's what we have to continue to understand with the guys that are out there.

"That's something that is never going to change about this team. Right now we are playing in spurts defensively; it's going to be tough if we don't start to develop some consistency on that end of the court."

Pierce could only shake his head looking at the final stat sheet. The Celtics shot a solid 50.6 percent, which was an appropriate figure because they were good for only a little more than half the game.

"It's about team defense, something we thrive on and hang our hat on," said Pierce. "It's just not a consistent night for a team to come in your building and shoot 50 or 60 percent. I look up and we shoot 50 percent -- most nights we win those games -- but when you allow a team to shoot that kind of percentage, it is going to be tough for any team to win ballgames."

The Celtics are second in the NBA in fewest points allowed per game (93.8), yet the last three home games have seen the Hawks, Bulls and Mavericks all soar above that mark. Opponents have averaged 44.5 percent shooting against the Celtics this season, but those three opponents have topped that mark during Boston's three-game home skid. None more impressively than the Mavericks.

The Celtics were expected to get a boost from the return of Rasheed Wallace -- and they did -- but foul trouble sidelined Wallace during Dallas' pivotal run.

The question following Monday's loss was whether the impending return of Kevin Garnett can fix what ails the Celtics. Coach Doc Rivers doesn't think it's that simple.

"Even if it does [fix the problems], everybody has to have better mental focus," stressed Rivers. "It can't be one guy. [Garnett's] voice will be back, but his actions have to return as well.

"Kevin's not in, so I'm not worried about Kevin. You know what I'm saying? He's not in right now and everybody else is. And they know their jobs. The voice of Kevin, yeah, it always helps because he holds everybody accountable. But that voice isn't out there right now and somebody else has to do it."

Celtics center Kendrick Perkins needed two stitches to close a gash below his eye caused by an inadvertent elbow by Dirk Nowitzki. It was the perfect symbol on a night the Celtics had no defense in the late rounds of a fight that was long over.

The Celtics' defensive problems actually might have started in the offensive end on Monday. Boston shot a woeful 36.8 percent (7-of-19) in the third quarter and Dallas attacked in transition.

"I think offensively, we put them in transition," said Ray Allen. "There was a stretch where we didn't get back at all and they had us playing on our heels. One side of the ball affects the other."

Rivers didn't have to remind his players that 24 minutes of good basketball isn't enough to beat a quality team.

"I told our guys I thought our mental focus and our mental toughness right now is not very good," said Rivers. "I thought the game plan in the first half was perfect. Get back in transition, contest shots and start inside-to-outside. Second half, I thought our defense was horrendous. I didn't think we got back at all on defense.

"[Dallas] had numbers every single time. We had our guards crashing the glass, trying to get offensive glass. Our bigs were complaining to the refs. They beat us down the floor and they scored. Then all of a sudden it became a walk-the-ball-up-the-floor, slow-down basketball game -- but one way. Then, on the other side, they were running it back down our throats. So I thought we had 24 minutes of focus, and it's tough to win a game that way against a quality team."

Even as his team fell to 11-7 at home -- surpassing the loss total of each of the past two seasons when the Celtics posted a 35-6 mark at the Garden -- Rivers said it was a matter of "when" his team starts playing better, not "if."

"I don't think it's a pattern, except for we're just playing poorly at home right now," said Rivers. "And we have to fix that. We will.

But 'when' is the question."

Chris Forsberg is a roving reporter for ESPNBoston.com. Follow him on Twitter.