Dirk Nowitzki had been relatively quiet for 47 minutes, silenced by a combination of his own lacking aggression and the long, active, disruptive arms of Kevin Garnett. Yet when Paul Pierce drilled a three-pointer to knot the score at 85-85 with 25.0 seconds remaining, I did not celebrate, but rather looked at my brother to say one sentence that would prove to be deadly prophetic: “I wish I could be happy, but this is usually Dirk time.”

The German has come many miles from the young kid with a reputation for shying away from pressure. Now an NBA champion, he has evolved into one of the most unstoppable clutch performers in the league, capable of getting his jumper off against anyone at any time but now also willing to put the ball on the floor and earn a bucket the hard way.

He chose the latter option against Boston, swinging the ball through Garnett’s pressure defense and taking a sharp angle to the hoop, every inch of his gangly arms and shaggy hair flopping underneath the TD Garden rafters, a lethal, if somewhat goofy, assassin who spends summers with a trainer calculating ways to maximize his effectiveness. Garnett’s intensity was a minor nuisance, but Nowitzki forced his way through, meeting Brandon Bass a foot away from the rim and muscling a hoop through contact. After the ensuing free throw went through the basket, Nowitzki had given the Mavericks an 88-85 lead. The Celtics would not get a chance to shoot for another tie because Rajon Rondo threw an inbounds pass off the shoelaces of Ray Allen, who had scooted around a screen and was open for three in the corner.

But the Celtics did not lose the game when the pass scooted out of bounds, and they did not lose it when Nowitzki bared his superhero cape. The Celtics started from the opening tap like they’d each just had three pounds of Mom’s lasagna and were fighting the urge to fall into a food coma right there on the parquet floor. They missed nine of their first 10 shots. Declined to rotate defensively. Didn’t show any intentions of rebounding. The Celtics shot 27.8 percent in the first quarter, surrendered 55 percent shooting and got outrebounded 13-8.

The bench — that much-maligned unit that hasn’t always been productive — brought them back, and did it the Celtic Way, with defense and excitement. Mickael Pietrus’ presence gave Boston three perimeter defenders capable of pressuring 94 feet from the basket, and Dallas had difficulty even getting into offensive sets against the Pietrus-Bradley-Dooling lineup. Since Doc Rivers chose to play Garnett many minutes with the second unit, and because Brandon Bass did more showing and rotating and hedging than he’d done all season, the C’s second unit looked downright scary defensively. There were some hiccups offensively — Bradley’s three-pointer that almost went straight through the backboard and killed a kid in the 15th row comes to mind — but the bench can still be credited for reinvigorating the Celtics when they needed flames sparked underneath their Nikes.

Defense continued to lead the way, and for spurts it was like the old days, with Garnett spearheading everything, calling out coverages to his teammates, and everyone else trying their damnedest to cut off opponent’s paths to the basket. It was the best Boston’s defense has looked this season, by a long shot, and they would take a brief lead in the third quarter on the backs of a defense that wouldn’t quit.

And then, before you could say “Jermaine O’Neal left to the locker room before halftime, take 78, but returned again at the start of the third quarter,” the defense quit. I’m not sure exactly when it happened, but it occurred midway through the third quarter, and I noticed it most blatantly when Chris Wilcox stood idly with his hands by his sides while Lamar Odom drained a triple with no contest. The Mavericks widened the gap into a double-digit lead, doing so more like a tank than a Ferrari, with the pace of a team that has been there, done that.

I’ve gotten to this point somehow mentioning Rondo only to discuss his late-game passing error, which isn’t fair to the man who was brilliant, repeatedly thrusting himself at the rim and by his defenders. Rondo was a one-man fast break, playing at a speed his own, in a universe by himself, a universe where nobody could stay in front of him, certainly not anybody wearing blue jerseys. Despite his brilliance, despite his 24 points, seven assists and three steals, it’s unsettling that no matter what Rondo does, I’m surprised. I’m surprised when he dominates and I’m surprised when he doesn’t; we never know what to expect from Boston’s floor leader on any given night.

The defense returned in the fourth quarter, Rondo’s one-man gang turned into the Paul Pierce show late, and the Celtics were *thisfreakingclose*to a gritty win against the defending world champions. But Pierce, who had awoken from his food coma to provide some late-game heroics, including the aforementioned tying three, left too much time for the German assassin whose late-game reputation has flipped on its head in recent years.

Fear the German. Fear Boston’s two spurts of effortless, execution-less play. But look closely at today’s game, and you’ll see a Celtics team that finally started to resemble the Celtics, if only for stretches at a time.