BOSTON — You had your chance, Eastern Conference. The Cavaliers were there – right freaking there – for the taking. LeBron was all but gone, Isaiah was awful and the locker room was as friendly as a “Real World” house after an all-night bender.

You had your chance – and now it’s gone. Cleveland’s 121-99 thumping of Boston on Sunday was a loud-and-clear message to the conference’s would-be champions: The Cavaliers are back.

Koby Altman was in the TD Garden on Sunday. A week ago, Altman was a 35-year-old managerial neophyte in over his head. You couldn’t go three paragraphs in a story about the Cavs’ struggles without reading some version of “Altman” and “was an assistant coach at Columbia five years ago” in the same sentence. Today? He should be in the running for Executive of the Year. Altman’s four trade deadline acquisitions– George Hill, Rodney Hood, Jordan Clarkson and Larry Nance Jr. – combined to post 49 points, 13 rebounds and five assists on Sunday. In their first game. With half a practice. Against the best team in the Eastern Conference.

Said J.R. Smith, “We looked phenomenal.”

Yup. In reshaping the roster two months before the playoffs – and to be fair, it’s easier to make moves like this when you have an owner willing to absorb bad contracts and a first-round pick to dangle – Cleveland has restored the natural order. Boston is a team on the rise, Toronto is battle tested and Milwaukee has been on a tear since Jason Kidd was shown the door. The Cavaliers? They’re the conference’s Death Star once again.

Here’s the thing about LeBron James: He doesn’t need great teammates. He needs teammates who do certain things great. Take Hill. No one is going to say Hill is more talented than Isaiah Thomas. But Hill is a dead-eye 3-point shooter with experience running successful teams. A year ago Hill averaged 15.6 points for the Jazz in the playoffs. Four years ago he was the floor general of Indiana’s back-to-back conference finals team. He won’t beat you off the dribble, but he will bury you in open threes. Guess which skill the Cavs need more?

Hood is quite simply one of the NBA’s most consistently underrated players. In college he averaged 16 points and made 42 percent of his threes. At Duke. His reward was watching James Young, Bruno Caboclo, Jordan Adams and 19 other players get drafted before him. In 39 games with Utah this season, Hood averaged 16.8 points (a career-best), made 38.9 percent of his threes (a career-best) and upped his free-throw percentage to – wait for it – a career-best 87.6 percent. At 25. He’s had some injury issues, but that the Cavs were able to nab Hood and Hill for Jae Crowder, Iman Shumpert, Derrick Rose and cash is highway robbery.

Inside the Cavs locker room, you got the feeling they know they stumbled upon something. They weren’t experiencing the same, old January swoon – Altman all but admitted it when he said the deals were made to stop the “slow death march” the team was on – so something had to give. But instead of a makeover, Cleveland has been reconstructed; instead of a cosmetic change, the Cavs have been fundamentally altered with a talent infusion that makes them conference frontrunners once again.

“I thought our spirit was different,” Cavs coach Tyronn Lue said. “I didn’t know what the outcome would be. But I knew we would compete and play hard. Move the basketball and move bodies. Those guys are flying around and it was good to see.”

Added James, “I know the guys that’s here, they’re very excited about this opportunity, and it’s my job to keep them excited about being here. They’re joining something that obviously the last couple months hasn’t been what we expected, but over the course of the last four years, since I came back, has been really good basketball. So it’s my job as the leader of this team to make sure that I acclimate the new four guys to be around a culture that’s built on winning and practicing championship habits. That’s it.”

That’s it? It could be. A lot could go wrong in two months, I guess. Hood could get hurt, Hill could look old and Clarkson and Nance could find making shots in meaningful games in May more difficult than firing up jumpers in a Lakers season going nowhere. Plus, with only about a third of the season left, practice time will be limited.

But the Cavs feel … different. They are younger, seemingly hungrier with the pieces a James-led team needs to be successful. Boston – which outclassed Cleveland on this same floor a month ago – has suddenly become tissue-paper soft, getting punched in the mouth by Toronto earlier in the week before letting the Cavs roll over them on Sunday. Cleveland may have rediscovered its mojo just as the Celtics are losing theirs.

As James walked off the floor, he crossed paths with Kevin Garnett, an old nemesis in town for Paul Pierce’s number retirement. Garnett – whose disdain for James during his playing days was both palpable and well known – shared a quick hug with him and, per ESPN, told James, “Ya’ll look so different.” Indeed. The days of the Cavs being pushovers could be over. The bully has returned to the block.