“I can imagine right now that Kevin Garnett and Paul Pierce and those guys are in there right now saying, 'Let’s deliver the knockout punch today.' This game, I think they feel like, if they beat us they can knock us out.” -- 76ers coach Doug Collins, an hour before tipoff.

At the All-Star break, the Celtics were 15-17 and coming off a five-game losing streak that included injuries to Brandon Bass and Jermaine O’Neal, Rajon Rondo’s two-game suspension for throwing a ball at an official and a series of horrific losses. They were four games behind Philadelphia in the Atlantic Division, and the only reason it wasn’t worse was because the Sixers also has lost five straight heading into the break.

The Celtics began to find themselves in March, while Philly continued to tread water. On March 23, they went to Philadelphia with a chance to take over first place in the division and lost by 13 points. It was after that game that the Celtics evolved into something else, ripping off seven wins in their next nine games, including Sunday night’s masterful 103-79 evisceration of Philly, which has lost 6-of-8.

The division once again belongs to Boston, which now has a three-game lead on the Sixers with 10 games to play. Philly, meanwhile, is in danger of missing the playoffs altogether. The Sixers are tied with the Knicks for the last two postseason spots and the Bucks are only a game behind and closing fast.

“It’s going to be interesting,” Collins said. “I think everybody’s sort of looking at Miami and Chicago as the two teams, but I wouldn’t blink on Boston. No, absolutely not. They can defend and they’ve got matchups.”

The defense is carrying the Celtics. Heading into Sunday’s game they ranked second in defensive efficiency behind Philly and will surely take over the top spot after that game is taken into account. Offensively, they rank next to last -- ahead of only the Bobcats.

“The defense has been really good,” Doc Rivers said. “Guys are just locked in. You know your offense will fail you. I don’t care how well you play, your offense is going to fail you sometimes. If you come with the right mindset, your defense never should and it will always give you a chance to win the game.”

The Sixers shot 38 percent and scored just 14 points in the second quarter and 16 in the fourth. Over the last dozen games, the Celtics have held their opponents below 40 percent shooting eight times. Over the last six, they have held four teams below 80 points.

“I think what you see is this is all coming together,” Kevin Garnett said. “I don’t want to say we’ve been shooting fairly well, overall we have been making some shots but we have some terrible nights shooting. As far as consistency, I think the defensive pressure has been there. I think for the most part the effort, the strategies, everybody understands the strategy of what we’re doing. It’s all coming together.”

Sunday’s game helped illustrate Garnett’s point. After a tight first quarter -- aided by five Celtics turnovers -- the much-maligned reserve unit blew the game wide open to start the second quarter when it outscored Philly, 17-4, over a six-minute stretch while Brandon Bass, Paul Pierce and Rajon Rondo rested. That group is now bolstered by the addition of Ray Allen, who scored eight points in nine minutes and seemed to be channeling the immortal Vinnie Johnson, aka The Microwave.

With Allen on the court with Garnett, Avery Bradley, Greg Stiemsma and a rejuvenated Sasha Pavlovic, the Celtics kept it simple. They threw it to Garnett in the post and had Bradley cut to the basket. If he slips through the defense, it’s two points. If he draws the attention, Garnett can kick it to Allen or Pavlovic on the perimeter or go to work down low. (Pavlovic has played well over the last seven games, but insert Mickael Pietrus into that lineup and it looks even better).

Allen is the key. With him coming off the bench, the Celtics now have balanced lineups, which is something they have been searching for since the 2009 season.

“We’ve talked about it for the last year and a half,” Rivers said about moving a starter to a reserve role. “We always wanted a stronger bench. Now with Avery and hopefully if we can get Mickael back, then it’s phenomenal. You have either guy you can play in the lineup and use the other guy off the bench. That would be the best-case scenario for us.”

Across the hall, Collins was wrestling with a lineup change of his own. When he moved Evan Turner into the starting lineup, his team was 22-16. Now its 29-27 and sinking fast. But Collins isn’t dealing with a veteran team that knows its time together is fleeting.

“Younger players are still carving their own niche, finding out who they are,” Collins said. “As a coach, piecing that together is a very difficult thing. The one thing with players today is they’re very sensitive. They’re very fragile. They didn’t grow up with tough coaches. You know, I had my ass kicked since I was 6. It’s a different time. I treat this team with kid gloves, and I’m still looked at as an ogre.”

Asked if it was difficult, Collins responded, “It’s terrible. It’s hard. It really is hard.”

It wasn’t lost on Collins that a 10-time All-Star like Allen volunteered to change his role or that a coach like Rivers felt compelled to go off on his team after a seven-point loss at Chicago on the second night of a back-to-back during its best stretch of basketball of the season. That’s the difference right now between Boston and Philly.

“It takes a real mature athlete if not a personality to accept the role,” Garnett said of Allen. “I think Ray’s done a good job with that, definitely exemplifying the excellence in everything that he’s achieved in this game with a sense of professionalism. It says a lot about who he is and it’s working for our team. Doc’s making moves on account of what’s best for our team, so right now we just have to play at this level.”

On paper, they are two good defensive teams that struggle to score points. In practice, one team knows exactly what it is and the other is searching for its identity at exactly the wrong time.