BOSTON — In the final moments of a perfunctory fourth quarter, as the Boston Celtics’ completed their demolition of the Indiana Pacers on Wednesday night, Boston rookie Robert Williams took a pass in the lane, dunked hard with two hands, then hung on the rim for a brief moment, if only to expel some velocity before returning to Earth’s orbit.



Referee John Goble assessed a quick-trigger technical, which seemed more like a scolding for the way the Celtics’ offense was unrelenting, making the scoreboard operator earn his paycheck during a 135-108 triumph at TD Garden.

One hundred, thirty five points. For a Celtics team that seemed to miss the memo about the NBA’s offensive explosion at the start of the season, that’s a jarring number. To do it against the second-best defense in the NBA — albeit one playing on the second night of a back-to-back and without game-changing big man Myles Turner — was even more astounding.

Maybe Boston’s recent offensive eruptions shouldn’t surprise us anymore. Maybe crisp ball movement culminating with made shots shouldn’t shock us. But it’s simply staggering how far these Celtics have come in such a short period of time.



Back in late November, just a short time after Kyrie Irving cussed out Thanksgiving, the Celtics sat 27th in the NBA with an anemic offensive rating of 104.6. Their offensive inconsistencies contributed to Boston's 10-10 record over those first 20 games and, if not for some very good defense, it could have been a lot worse when you consider the three teams behind Boston in offensive efficiency at that point were a combined 13-46 (.220 winning percentage).



But on Nov. 26, with injuries forcing his hand a bit, Celtics coach Brad Stevens elevated Marcus Smart and Marcus Morris to starting roles in hopes of providing the energy jolt the Celtics so clearly needed. Even Stevens probably couldn’t have anticipated what has happened since.



Over the last 20 games, Boston owns the NBA’s top offensive rating in averaging 117.4 points per 100 possessions. That’s 2 points better than their nearest competition (the James Harden-fueled Rockets) in that span. It’s also 3.7 points better than the Golden State Warriors’ NBA-leading offensive rating of 113.7 for the season.



CHART: TALE OF TWO QUARTERS



The Celtics have turned their offense around the past 20 games. A look at the key numbers (with NBA rank in parentheses):



First 20 games Last 20 games

Offensive rating 104.6 (27th) 117.4 (1st)

Points per game 106.3 (24th) 118.7 (1st)

Assists per game 24.3 (11th) 28.4 (1st)

Record 10-10 15-5



During the early part of the season, it felt like the Celtics jumped on Irving’s back and asked him to keep them afloat with Irving seemingly the only player immune to Boston’s offensive woes earlier in the year.



On Wednesday night, Irving got a breezy fourth quarter. He could have kicked his feet up, instead he stood for much of the quarter to celebrate everything from Williams’ volleyball-style blocks to Semi Ojeleye’s Eurostep layup. For the first time this season, it feels like the Celtics are clicking on nearly all cylinders, putting at least seven players in double figures each of the past two games.



And Irving is having fun being a spectator at times.



“Real fun,” said Irving. "Making shots helps, helps cover up a lot of mistakes. But we’re just playing extremely well off the ball. On the ball making good decisions. Just the ball’s not sticking. Guys are getting to spots and making the most out of their opportunities when they get it. So just creating for one another and just making the right pass.”



It sounds so simple but for much of the first quarter of the season, the Celtics fought themselves. There were obvious growing pains reintegrating a healthy Irving and Gordon Hayward, while younger players struggled to identify and embrace their new reduced roles. When shots didn’t fall, heads hung, and Boston routinely endured the sort of lapses that contributed to a .500 start.



But the past month-plus has delivered some exquisite basketball. Smart didn’t just infuse energy, he brought the first unit a player who was happier to facilitate than fight for shots (though his increased 3-point efficiency has certainly aided the Celtics at times as well). Morris has played his way into All-Star consideration regardless of his role and now, finally, the rest of the roster is catching up.



Hayward is showing more confidence, more aggression. Jaylen Brown knows good things happen when he attacks the basket. Tatum can have stretches like the start of the Indiana game where he just dominates with his length and touch.



Impossibly, the Celtics are now an offensive juggernaut. In 45 days they’ve gone from lingering on the basement steps to clawing their way into the top 10 in offensive rating. Boston now sits ninth overall with an offensive rating of 110.9 for the season.



So what in the world got into these Celtics?



“When we’re making shots and we’re continuing to make each other better and making those plays that we weren’t making at the beginning of the season, just trusting one another in specific positions in our offense,” said Irving. "At this point I feel like we’re very comfortable in what we’re running, and guys being in specific spots, and opportunities that we can take advantage of, and passes being delivered on time, and just caring about the pass and caring about your teammate making a shot.



"So everything we talked about at the beginning of the season, I feel like it’s translating now as we continue to get to know one another. Meat of the season right now and you can tell that our team is just feeling really good being around each other. And it’s totally different in terms of how we feel out there. It’s just really positive. And when I don’t have to go out there and score 30 it’s cool with me. I probably won’t have to score 30 until we play one of the best teams in the league — if any — [or] until the playoffs. So I’m happy about that.”



Irving wasn’t always happy. But he was unfailingly patient. Asked about the well-publicized team meeting in December, he admitted, "We could pinpoint a lot of turning points. … We weren’t at rock bottom but we needed to address some s--- in this locker room.” It didn’t cause the offensive turnaround but it didn’t hinder maybe the final step in that process, with younger players starting to accept their smaller roles.



Is this sort of offensive production sustainable? Probably not. And Boston would be well-served to tighten up a defense that has tended to slip a bit whenever the offense is thriving (the absence of players like big man Aron Baynes hasn’t helped either).



But a four-game winning streak leaves Boston feeling some good vibes. The offense is clicking and players are able to operate more freely, not lingering on what isn’t going right like they did earlier this season.



"As you can see, we're having a lot of fun — especially when you win,” said Tatum. "So if we just keep winning, we'll keep having fun.”

Click here to download the new MyTeams App by NBC Sports! Receive comprehensive coverage of your teams and stream the Celtics easily on your device.