Boston ? LeBron James played as if he were tired of all the panic.

An 18-point home loss to the Boston Celtics in Game 2 of the Eastern Conference semifinals opened the door to three days of hysteria.

Would the Cavs’ big dreams die before the playoffs were barely a fortnight old?

Was “The Elbow” an extension of Cleveland’s professional sports curse?

And just how many MRIs has James had, anyway?

James came out almost angry Friday night in Game 3 against the Celtics in TD Garden. With friends Jay-Z and Beyonce watching courtside, James poured in 21 points in the first quarter, making eight of 10 shots from the field. He outscored the Celtics by four in the first 12 minutes. Thanks to the early domination James provided and the Cavs’ 61.5 percent shooting in the first half, they rolled to a 124-95 victory.

“It was great to see LeBron set the tone from the jump ball and the other guys follow,” Cavs coach Mike Brown said.

“In the first quarter … we didn’t have anybody to respond to him,” Celtics coach Doc Rivers said.

It was an amazing start for James, who bombed in 38 points in 39 minutes, making 14 of 22 shots before going to the bench with 5:41 remaining.

“You knew he was going to grab the ball and attack,” Rivers said of James. “I didn’t know he wasn’t going to get any resistance. He was playing H-O-R-S-E.”

Almost as if to answer the questions about his sore right elbow (which has had only one MRI, by the way, a question sparked by Brown’s and a team spokesman’s mistake), James’ first shot was a beautiful 16-foot turnaround jumper.

Five of his first eight baskets were jumpers, which James had been hesitant to take, especially in the first half of Games 1 and 2.

But James was on fire on this night, and you could cut the air of invincibility with a knife.

“It was much bigger than what it really was,” James said of the elbow frenzy. “All the media circus, I wasn’t tired of that at all.

“My focus was on Game 3. It was a really important game for us. Aggression was my mind-set, to dictate the tempo from the start.”

When the second quarter began, the newly crowned two-time league Most Valuable Player did not start it on the bench as has been his tradition.

The barrage continued.

James finished the first half with 28 points, missing only four out of 15 field-goal attempts.

“He’s our leader,” Cavs forward Antawn Jamison said of James. “He was really focused coming into today’s shootaround. When he goes, we go.

“Early, he was aggressive going to the hole, defensively really setting the tone.”

Rivers believes it’s time to make the focus something other than the most famous elbow in America.

“I think he’s healthy,” Rivers said of James. “His elbow looked very good tonight. Enough with the elbow injury. I think he’s healthy, now we can focus on basketball.”

By midway through the third quarter Friday, when James had surpassed his 35-point effort of Game 1, Celtics fans were taking snapshots of James just to remember what they’d seen.

The Cavaliers’ lack of intensity had been replaced by a collective sense of purpose.

All panic was forgotten. Or at least shelved for another day.