Shortly after the Celtics learned Rajon Rondo was lost for the season, reality set in:

They would need to change — fast.

Without a point guard who dominated the ball, the Celtics required someone to steer the offense. But instead of giving that responsibility to one player, they gave it to several — consolidation, as Kevin Garnett has repeatedly said.

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This teamwide involvement helped others who didn’t handle the ball get into a rhythm during games. Key examples are Leandro Barbosa, Jason Terry, Jeff Green, and Courtney Lee, who combined are averaging 13 more points per game in the last six games (all wins) since Rondo, who was averaging about 14 points himself, went down.

It has also meant more minutes for players whose roles weren’t as defined.

“That definitely helps,” Lee said, “because when you don’t know how many minutes you’re going to get, you play helter-skelter and force a lot of stuff and force the action. Now, we’re comfortable, the rotation is set. We’re in our zone, so it works out for us.”

The team had often relied on Rondo to create shots, score, etc., which at times made the rest of them “lackadaisical,” as Garnett said Thursday night after his team pounded the Lakers at TD Garden, 116-95.

Yet with Rondo out, they realized they could no longer be lackadaisical. They would have to create shots for themselves and each other. But how? Coach Doc Rivers didn’t have a grand scheme. He kept it simple, telling them to quickly pass until an open look appeared.

“We almost feel like we’re playing summer ball; if you don’t have anything, just pass it, pass it, pass it,” guard Avery Bradley said. “It’s hard to beat a team like that.”

But the Celtics are doing more than just passing. They’re passing at a rapid pace, partly because Rivers wants to speed up the game to run what he has deemed a “spread offense,” like in football. This pace is actually more akin to a no-huddle spread offense.

It can be that fast.

That speed came in the third quarter Thursday, when the Celtics scored 31 points in 6:08 to double their 13-point lead and basically decide the outcome.

Just before Rondo went out, though, the Celtics were coming together on defense. It helped that Bradley, their best defender and leader on that end, returned in January from an injury. His aggression has proven contagious, and Boston’s improved defense has taken pressure off its offense to score.

And as the defense was picking up, that, in turn, blended well with this new, up-tempo ball-movement offense. The Celtics would grab a defensive rebound, immediately pass it up the floor to an outlet guard, who would then look up court for a quick pass that could lead to an open shot.

This style of play has kept defenses on their heels, and has helped the Celtics average 102.8 points during their six-game winning streak, a significant boost from the nearly 95 points they averaged before Rondo went out.

Another key aspect is the schedule. Aside from Miami, the Celtics have played five struggling teams during this streak. Sacramento, Orlando, Toronto, and the Lakers were a combined 46 games under .500, and the Clippers were without their best player, point guard Chris Paul.

A relatively easy stretch of games — five at home — was the perfect set-up for the Celtics to implement this new style.

Against Toronto, in fact, the Celtics strayed from their style in the second half and wound up down by double-digit points. Rivers said he thought that moment “in a crazy way was really important for our team, because they visually identified what they shouldn’t do and how they can’t play.

“And you could hear them talking about it throughout the game, ‘This is not us, this is not us,’” Rivers continued. “You kept hearing it, all game. And then when we finally got the pace, then you could hear them, ‘This is who we are.’

“I thought that was big for us to see it visually. I could say it and show it on film, but when they saw it, I thought that was great.”

Of course, there is still much debate about whether the Celtics are better off without Rondo. With him on the court, the Celtics’ effective field goal percentage is 49.4; with him on the bench, it’s 49.9. The Celtics’ offensive rating (per 100 possessions) with him is 99.2; without him, it’s 102.6. And the team is averaging 93.8 points with him, 93.8 points without him. The differences aren’t that large, and, even then, the sample size isn’t large enough for a true comparison.

Those numbers combine when Rondo has been on the bench and when he hasn’t played, so they don’t exactly reflect how the Celtics have played since he was lost for the season. Moreover, because the competition has been weak, it hasn’t been easy to gauge the team’s standing in the last six games.

“They are not a better team [without Rondo] but they are playing better,” TNT NBA analyst Kenny Smith said. “There is a sense of urgency. The reason is a lot of their guys aren’t skill guys, they’re effort guys. Their effort and energy are being showcased now . . . with Rondo, it wasn’t.”

Rivers said this week that Rondo could fit into this new scheme and that he would consider using it when he returns. Would it look the same with Rondo at the point?

“It should,” Rivers said. “I think he would have the ball less at times. He would do more cutting and spacing, but yeah.”

However this Celtics season turns out, the system they installed in response to Rondo’s absence could well be the system they use in the future. And if the results continue to be as promising as they have been, that future could be bright.

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The Celtics assigned 7-foot center Fab Melo to their NBA Development League affiliate, the Maine Red Claws.

Melo played a total of eight minutes against the Magic and Lakers, and had 2 points, 1 steal, and 1 block.