BOSTON — So much for the Cleveland Cavaliers’ late-season defensive woes. So much for any lingering rust from a restful break between series. So much for the East presenting a challenge to LeBron James.

The Cavs left no doubt the proverbial playoff switch had been flipped, lighting up the top-seeded Boston Celtics at TD Garden in a 117-104 win in Wednesday’s Game 1 of the Eastern Conference finals. Kyrie Irving was an afterthought, and Cleveland got little help from its bench, but none of it mattered, because they have LeBron, who paired 38 points, nine rebounds and seven assists with a defensive effort that strangled Boston in a game that wasn’t nearly as close as the final score indicated.

“You’ve got to tip your hat to them,” said Celtics star Isaiah Thomas, who scored 17 points on 19 shots and added 10 assists. “They were the better team tonight, and they had more energy than us. It was obvious. They had a week or two off, and we just went seven games. We can’t use it as an excuse, but they hit us first, and they were the more energized team tonight. There was a reason for that.”

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James’ frontcourt partners Kevin Love (32 points, 12 rebounds) and Tristan Thompson (20 points, nine rebounds, six on the offensive glass) did the rest of the damage. The scariest part? The Cavs could probably play better. The Celtics have plenty to solve before Game 2 on Friday night at 8:30 p.m. ET.

“I don’t even think we played that great tonight,” said James, sending shivers down Boston’s spine.

“Tonight we were pretty good on the defensive end,” Love said of a defensive performance that held Boston to 36 percent shooting in the first half, including 2-of-16 from 3-point range. “We felt like we could’ve played better, and there’s some things we’ll look at tomorrow that we’ll be better for Friday.”

On the same postgame press conference podium moments earlier, Celtics coach Brad Stevens conceded to the dilemma every Eastern Conference coach has faced for the better part of a decade now — they have nobody who can defend LeBron 1-on-1, and they can’t double-team him, for fear of Cleveland’s bevy of sharpshooters. “This is the predicament they put you in,” said Stevens.

The Celtics are better than they were when the Cavaliers swept them in the first round of the 2015 playoffs, but so too is LeBron, and the gap between the two doesn’t appear to be all that different.

“It’s hard to believe, but he’s better than when I got into the league. A lot better,” added the fourth-year Celtics coach. “Just as you get older, you gain more experiences, you see more things. Yeah, I didn’t think he could get any better after that, but he is. He’s a good player. Great player.”

If ever there was a game for the C’s to steal, it was this one at home, riding high on a 48-hour stretch that featured wins in Game 7 against the Washington Wizards and the draft lottery, against a team that hadn’t played since May 7. But no. James picked Boston apart, as he’s now done now for two different teams in four separate playoff series against a pair of Celtics adaptations over the past six years.

It was immediately apparent that the nine days of rest resulting from sweeps of the Indiana Pacers and Toronto Raptors only did the Cavaliers more good. On the opening possession of Game 1, the Cavs trapped Thomas in the corner. He had two options — turn the ball over or let the final seconds tick off the shot clock. When he chose the former, Irving answered with a layup on the other end.

Every concern the Celtics had entering the series hit them full force in the face from the start. Defending the Cavs on one possession is a tall enough task, and it becomes nearly impossible when you grant them second chances. As ever, Cavs center Tristan Thompson continued to own Boston on the glass, grabbing four offensive boards in the opening quarter alone — just as the Wizards’ Marcin Gortat had done to the C’s last series, and just as Chicago’s Robin Lopez did in the opening round.

“Tristan was big. He’s our energy. He’s our motor,” Cleveland coach Tyronn Lue said of Thompson’s ability to rule the rim at both ends. “I think his physicality is huge for us, especially against this team.”

Meanwhile, Boston had no answer for LeBron. He scored 15 points on 7-of-8 shooting in the first quarter and toyed with Game 7 hero Kelly Olynyk, one of several pick-and-roll switch victims:

Just as he’d done by calling for an off-the-backboard alley-oop, spinning the ball several times before draining a 3 over Serge Ibaka and taking a faux swig off a beer in Game 1 against the Toronto Raptors in the last round, James showed a complete lack of regard for his latest conference foe. James ran his playoff record against East opponents to 33-4 since returning to Cleveland, and barely broke a sweat.

“It was very clear that he was trying to get to the rim on us no matter who was on him,” Stevens said.

Stevens reached 10 deep into his roster in the early going, even trying Tyler Zeller, and couldn’t find a solution to stop the bleeding. When LeBron wasn’t getting to the rim at will, he found teammates for more layups, opening the door for the barrage of wide-open 3-pointers to come in the second half.

“Obviously, he’s a great scorer, and when he gets going downhill, he just has to see bodies,” said Celtics forward Jae Crowder (21 points, eight rebounds, five assists), who served as the primary defender opposite LeBron. “I have to do a better job of being up to touch on him, being on the ball, making it tough for him. But he has to see bodies behind me. We have to do a better job of showing help early, then getting out and spreading out to the shooters so they won’t be a factor in the game.”

As Stevens said, though, “This is easier said than done.”

James fully recognizes the predicament he presents, and that’s the most dangerous part of trying to contain him for 42 minutes. “It’s not an individual matchup for me, no matter who’s in front of me,” he said. “My mind is always racing on how I can make this the best possession at that particular time.”

For their part, the Celtics started 1-for-15 from the 3-point line and couldn’t generate any offense outside of Avery Bradley’s arsenal of jumpers and backdoor cuts (he ultimately matched Crowder’s team-high 21 points), and some inspired play off the bench by rookie Jaylen Brown (10 points, nine rebounds). As a result, the Cavs had built their double-digit lead, 30-19, by the end of the first quarter, and they didn’t even make their first 3-pointer until 3:33 into the second — so things only got worse.

Thomas’ years-long struggles against the Cavs continued. He started 2-for-10 from the field, only knocking down his first 3 as the buzzer sounded on the first half. By then, Cleveland was up 61-39.

“I just missed shots, didn’t get a rhythm,” said Thomas, who attempted only three free throws. “But next game I’ll definitely be more aggressive to make plays, get in the paint and make stuff happen.”

Cleveland’s lead swelled to 28 in the third quarter, when Love caught fire and knocked down five of his seven 3-point attempts in the frame. For the better part of three quarters, the Celtics and their crowd appeared lifeless, until Marcus Smart reentered the game and started doing Marcus Smart things. The C’s bulldog got under Thompson’s skin, created turnovers and collected three assists before closing out the third quarter with a put-back dunk that capped a 15-4 run and cut the deficit to 92-75.

Things got testy between the two teams. A frustrated Thomas may or may not have swiped at Love’s ankle from his backside (“I didn’t see it,” said Love, “truthfully”); Smart and Thompson exchanged double personal fouls during a dust-up; and then Thomas and Thompson got into it a bit. So, Irving, whose 11 points (on 4-of-11 shooting) were hardly needed, reminded the Celtics of the score:

Smart’s fourth-quarter presence, though, was as fleeting as the life he breathed back into the Garden at the end of the third. The Cavs pushed the lead back to 20, and his scrappiness caught up to him as he committed his sixth foul with nine minutes still left in the game. The Celtics got within 16 with four minutes to go, but by then, any hope of a comeback had joined the fans on their way out the building.

A minute later, Stevens waved the white flag, inserting James Young and company off the end of his bench, even though Game 1 was over almost as soon as it started. And Game 2 is around the corner.

“Whenever their backs are up against the wall, they tend to play better, just like we do,” said Cavs guard J.R. Smith. “We just got to expect that and understand there might be dirty plays, might be cheap shots coming from the other side, just because they are fighting for their lives at this point.”

Yup, the Cavs are looking for a challenge. They just haven’t seen one yet in the Eastern Conference.

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Ben Rohrbach is a contributor for Ball Don’t Lie and Shutdown Corner on Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach