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.

View photos LeBron James is energized in a blowout win over the Celtics in Boston. (Getty) More

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.

View photos Cleveland Cavaliers’ LeBron James plays against the Boston Celtics during the third quarter of an NBA basketball game in Boston. The Cavaliers won 121-99. (AP) More

“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.”

Story continues