BOSTON — LeBron James did pretty much whatever he wanted to against the Boston Celtics in the Cleveland Cavaliers’ dominating win in Game 1 of the Eastern Conference finals.

He was efficient, scoring from the outside, rolling downhill and getting to the rim at will, passing to teammates and locking down Boston scorers when called upon.

With home-court advantage gone, the Celtics face a virtual must-win Game 2 on Friday night. Boston must find a way to slow down James while not getting eaten up by a supporting cast, which other than Kevin Love’s big game, didn’t produce at its usual high rate.

Oh, and there’s extra motivation for Cleveland – now 9-0 in these playoffs – which could earn another long rest if it makes quick work of the Celtics.

But here’s the rub for top-seeded Boston on Friday night: James said he wasn’t even playing at peak condition after Cleveland’s 10-day layoff between rounds.

“I felt OK last night,” James said Thursday. “I knew I wouldn’t feel that great after the game, and I don’t feel that great right now. … But I should be much better (Friday).”

Better than 38 points, nine rebounds and seven assists? Good luck with that, Boston.

Still, James said the Cavs are mentally preparing for the Celtics’ best shot in Game 2.

“There’s going to be some adjustments made from both sides. We have to be ready for it,” he said. “Obviously we don’t know the exact adjustments, but we know they’re going to make adjustments. That’s what good teams do and we have to be ready for whatever they bring to the table.”

Most of the damage in Game 1 was done by only two players – James and Love. Kyrie Irving had just 11 points on 4-of-11 shooting, and usually dependable sharpshooters J.R. Smith and Kyle Korver were a combined 2 of 8 as Coach Tyronn Lue used a different second unit to start the second quarter with James resting.

A loss Friday also would leave Boston with the daunting proposition of having to win four out of five games to take the series – a nearly impossible task against a team that, since James returned to Cleveland in 2014-15, has a 33-4 playoff record against Eastern Conference opponents.

Celtics Coach Brad Stevens said his optimism remains high and he was “really encouraged” by his team’s performance over the final 18 minutes. It included getting within 11 points with less than two minutes to play.

But if the Celtics are going to pick themselves up, it must start with Isaiah Thomas, who scored 17 points but had to work for every one just to finish 7 of 19 from the field. He also had a team-high four turnovers – another red flag for Boston’s prospects. For his part, Thomas said there doesn’t need to be a lot of soul searching.

“There’s nothing to figure out,” Thomas said. “They play their traditional way. I mean, they definitely showed a few bodies that was aggressive on me, but that’s nothing I haven’t seen this whole year. I mean, I’ve seen it all … I’ve just got to be more aggressive, make plays, make shots and go from there.”

A bigger problem for Boston is that James scored on all seven defenders the Celtics threw at him in Game 1 – Crowder, Thomas, Marcus Smart, Al Horford, Jaylen Brown, Gerald Green and Kelly Olynyk.

Conversely, James has shown an ability to completely stifle Thomas on the defensive end. On the lone one-on-one possession in which Thomas was guarded by James – in the second quarter – Thomas was called for a traveling violation after James cut off his driving lane, contested his awkward layup attempt and forced Thomas to catch his own shot, resulting in a turnover.

And even if Thomas can rediscover his shot, he will need more scoring help against the Cavs’ Big Three. It’s a luxury not lost on Lue.

“Any given night it could be Kyrie, could be LeBron, could be Kevin, Korver, J.R. (Smith), Tristan (Thompson),” Lue said. “So we just take what the defense gives us and that’s how we try to play. And whatever guys are doing, we try to ride the hot hand and everyone else will fill in.”