NBA

Nets’ December struggles continue with Christmas loss to Celtics

Santa brought the Nets a hi-def TV appointment, sleek monochrome uniforms, an alarm clock (with snooze button) and a Kevin Garnett dartboard.

Brooklyn’s nationally-televised noon Christmas Day showcase went from a gift to a hassle when the sleepy-looking Nets were shoved aside by the Celtics, 93-76, Tuesday in front of a sellout crowd of 17,732 at Barclays Center.

The sputtering Nets (14-13) fell to 3-9 in December with four games remaining in the final six days, beginning Wednesday night in Milwaukee, as they try to prevent their debut city campaign from going off the rails.

“[The Celtics] had that look in their eye like it was really, really important — when things went bad on their end of the floor, they stuck with it,” Nets coach Avery Johnson said. “We dropped our heads a little bit. That’s something that I’ll visit with our team about. When something goes wrong, that’s when you really have to get tougher.”

Things got testy with 9:31 remaining when Gerald Wallace got tangled up with — who else? — Garnett, the Hall of Fame instigator who was also in the thick of a melee when the teams last met Nov. 28. Wallace grabbed a fistful of Garnett’s shorts as he stumbled after a whistle and the teams engaged in the customary pushing and posturing.

Wallace, Garnett, Andray Blatche and Courtney Lee were assessed offsetting technical fouls. Jared Sullinger added some more spice to the egg nog with a flagrant foul to take away a layup from Wallace with 6:03 left.

The Nets should have been more enraged by their futility on offense. They failed to crack 20 points in any of the final three quarters, shooting 40.6 percent from the field, missing 12 of 29 free-throw tries and committing a ghastly 20 turnovers. Deron Williams, facing waves of double teams, took just seven shots and finished with 10 points. Wallace and Brook Lopez shared the team-high with 15 points.

“We just couldn’t get anything going offensively,” Williams said. “Their defense picked up and made it hard for us. They were really physical with us. … Our shots weren’t going, I think because they were being so physical with us.”

The game hinged on a 23-5 second-quarter Celtics run that turned a tentative three-point Nets lead into a 49-34 deficit in the span of 6:26. Though Johnson reinserted most of his starters about halfway through the spurt, Boston was able to shoot 9-of-13 from the field and grab 10 rebounds to take command.

“We’ve just had some issues when we try to sub our starters out,” Johnson said. “We’ve had some inconsistency when we substitute, so we have to try to figure that out.”

The Nets mounted a third-quarter comeback from the depths of a 21-point hole, tightening the game to 66-58 with a 15-2 run highlighted by two Joe Johnson 3-balls, the second of which he launched from the vicinity of Park Slope. But Rajon Rondo (19 points, six rebounds, five assists) drew a charge, handed out an assist and nailed a rare 3-pointer in the final 1:13 of the quarter to push the Celtics’ cushion back to 15 and all but end it. The Celtics, the league’s worst rebounding team, held a 41-36 advantage on the glass.

The Nets now turn around and head out of town to face the Bucks, looking to get out of their rut and trying to dispel the impression they are not ready for prime time after a dud in their holiday litmus test.

“We need a win to take away this loss,” Williams said. “This leaves us a sour taste in our mouths, so hopefully we can come out and play with a little more energy and consistency.”

jlehman@nypost.com