Rajon Rondo  missed a wide-open 3-pointer to win it, and Kevin Garnett  missed a fadeaway jumper to tie it in the final seconds. Paul Pierce  scored a team-high 24 points, Garnett added 18 points and 15 rebounds, and Rondo produced 11 points, 15 assists and six rebounds for the C’s, who fell to 6-2.
Nowitzki led the Mavericks (4-2) with 25 points, six rebounds and four assists.
THREE THINGS THAT WENT WRONG
1. First-half defense: You’re probably not going to beat anybody — let alone the Mavericks — when you allow an opponent to shoot 55 percent from the field for the first half. Dallas made 21-of-38 field goals in the opening 24 minutes, building a lead as large as 14, en route to a 10-point halftime lead.
Mavericks big men Tyson Chandler  and Nowitzki were the biggest benefactors of the C’s porous defense. Chandler finished 5-for-5 in the first half, scoring all 10 of those points within two feet of the basket. Nowitzki scored nine first-half points on 4-of-7 shooting.
2. Shooting: It’s bad enough when you allow 55 percent shooting, but it hurts twice as much when your own field-goal percentage is hovering around 35 percent for much of the night. A second-half streak only raised the Celtics’ field goal percentage to 41 percent for the night.
3. Losing the free-throw battle: Sure, the Celtics shot 100 percent from the free-throw line, but they only had seven attempts. The C’s got just one free-throw attempt combined from Glen Davis, Jermaine O’Neal, Garnett and Rondo.
Meanwhile, the Mavericks shot 20 free throws, making 17 (85 percent). Nowitzki alone matched the entire Celtics roster from the free-throw line, making all seven of his attempts. For the referees’ sake, it’s a good thing Tommy Heinsohn didn’t make the trip.
THREE THINGS THAT WENT RIGHT
1. The halftime speech must’ve worked: The Celtics were badly outplayed in the first half and lucky to be trailing by just 10 at the break. The few signs of grit the C’s showed in the opening 24 minutes didn’t pay dividends, as their own shots just weren’t falling.
Well, something clicked, as the Celtics went on a 22-9 run to start the second half, taking a three-point lead on a trey from (who else but) Ray Allen just 8:14 into the third quarter.
2. Team rebounding: Jermaine O’Neal may have left the game at halftime because of his ailing left knee, but the Celtics didn’t miss him. Garnett grabbed a team-high 15 rebounds, while Pierce (7 boards), Rondo (6) and Allen (5) also chipped in on the glass.
In all, the Celtics out-rebounded the Mavericks, 41-38.
3. Semih Erden continues to contribute: In Jermaine O’Neal’s absence, Semih Erden played 11 minutes, scoring six points on 2-of-4 shooting from the field and 2-for-2 shooting from the free-throw line.
Erden has yet to miss a free throw this season, entering Monday night’s game a perfect 7-for-7 from the charity stripe. Perhaps that production can offset any struggles Shaquille O’Neal  has at the line this season.