Rising toward the rim, LeBron James cocked his right arm and unleashed four games of frustration on the Boston Celtics.

He’s had better dunks. Higher. Harder. Dunks of all shapes and sizes.

None, though, as satisfying.

“There was a lot built up,” he said. “That was the play we needed.”

James scored 21 points, the final two coming on a devastating slam over Kevin Garnett in the final two minutes, as the Cleveland Cavaliers beat the homesick Celtics 88-77 in Game 4 on Monday night to tie the Eastern Conference semifinal at 2-2.

Back even, and back to Boston — with authority.

James shook off one of the worst shooting slumps of his life by dominating down the stretch. He finished with 13 assists — four in the fourth quarter — and sent the Celtics to their fifth straight road loss in the postseason with a thunderous windmill knockout dunk.

“That,” Wally Szczerbiak said, “was phenomenal.”

So was the Cavaliers’ defense. Cleveland held the Celtics, the NBA’s best defensive team, to just 12 points in the final period on 5-of-16 shooting and 39 percent shooting overall.

“We’ve been able to cover for each other, flying around and contest at the same time,” James said. “It’s been amazing.”

Boston dropped to 0-5 on the road in the postseason, a stunning slip for a team that went 31-10 away from their home floor during the regular season. During a short stay in Ohio, the Celtics lost their momentum in the series but will now head home, where they went 35-6 before the playoffs started.

What’s the problem?

“It’s hard to say. I have no answer for it,” Boston’s Ray Allen said.

Game 5 is Wednesday night, and Game 6 will be back in Cleveland on Friday.

James was 7-for-20 from the floor, but he did everything else for the Cavs, who are attempting to overcome an 0-2 deficit for the second time in two years.