CLEVELAND -- Of LeBron James' many attributes, one that was easily taken for granted over the past seven or so years is the perception that he is immune to having bad playoff games.

He had one Sunday night, a dud that opened the door for the Boston Celtics to score the most improbable victory of the playoffs to this point. Boston completed a 21-point comeback against the Cleveland Cavaliers by winning 111-108 on a 3-pointer by Avery Bradley with 0.1 seconds left to pull the suddenly interesting Eastern Conference finals to 2-1.

James had just 11 points, of which only three came in the second half as he went 1-of-9 shooting and had an unusual vanishing act when his team needed him.

"I had a tough game, period. Not just in the second half," James said. "I didn't have it. That's all I've got to say about my performance."

James has had a few bad playoff performances in his career. There was the 2-of-18 shooting game in Boston in 2008. The mysterious, low-energy Game 5 against the Celtics in 2010, in which he was a stunning nonfactor. Of course, the failure in Game 4 of the 2011 Finals in Dallas, when he managed just eight points.

They're easy to recall because they're so rare.

James has been as reliable in the spring as the rain ever since, delivering time and time and time again. Over the past month, he'd never been better, racking up nine straight 30-point games to tie a Michael Jordan record and 10 straight games of 25 points and 50 percent shooting, a Kareem Abdul-Jabbar record. He's never been hotter.

Which made what happened Sunday so remarkable. Not just that the Celtics broke the Cavs' 13-game playoff win streak. Not just that they did it without the injured Isaiah Thomas. Not that they came back from being 21 points down with 19 minutes left. (James’ teams had been 49-0 when leading a playoff game by 20 points or more, according to ESPN Stats and Information.)

A closer look at all that went right for the Celtics and what went wrong for the Cavaliers to close Game 3 of the Conference Finals pic.twitter.com/4Fu5WqhSde

— ESPN Stats & Info (@ESPNStatsInfo) May 22, 2017

James got beat on rebounds. He seemed to not want the ball in the fourth quarter, giving it up and standing away from plays like he'd taken a time capsule back to his unsteady years.

To be sure, the Celtics were fantastic down the stretch. Needing scoring badly, they caught fire from outside, making 11 of 22 3-pointers in the second half while the once-hot Cavs had their weapon stolen, going just 2-of-17 in the second half from beyond the arc.

Marcus Smart, who drew the start in place of Thomas, had one of the best games of his career, finishing with 27 points and making 7 of 10 3-pointers. He was the scoring engine in the second half, putting up 19 and inspiring his teammates with fearless play.

Bradley had 20 points and hit his second game-winner in Cleveland over the past two seasons. It was the result of a clever play Celtics coach Brad Stevens designed, one of three perfectly executed plays in the final two minutes that the Celtics ran out of timeouts.

"We were playing way better. I don't know how to phrase it other than that. We were playing way better," Stevens said. "We were getting good shots on offense and playing with great purpose, and on defense I thought we were much better than the score indicated. I think that when you play better, you feel better. And you just kind of stay the course."

Kevin Love had a brilliant game with 28 points and 10 rebounds, but he also missed a wide-open late 3 when it really mattered. Kyrie Irving was equally excellent with 29 points and seven assists. On this night, James' supporting cast could not be blamed.

Jonas Jerebko, who had been used only in mop-up duty over the first two games, was a Brad Stevens last-ditch attempt at changing the game's direction that worked brilliantly. He sent him in for Al Horford with seven minutes left in the third quarter and the Cavs holding a 21-point lead, their biggest of the game.

Jerebko delivered the kind of energy and abandon the Celtics had been missing. He made only four baskets, but he got five rebounds and started getting under the Cavs' skin. Within minutes, he tussled with Love, Kyle Korver and Deron Williams. It seemed to help turn the tide.

Over and over the window opened for James to put a stop to it, but he never did. It was just the second time in his playoff career he played the entire fourth quarter and failed to score, the last time being that infamous eight-point game in 2011.

James’ frustration at his performance showed up after the game when he had an encounter with a heckling fan in the hallway outside the news conference room and then challenged a local radio reporter on a question he didn’t care for.

"He's human, so he's going to have a night like this," Cavs coach Tyronn Lue said. "He didn't shoot the ball well, and we still had a 20-point lead. A game we should have won, but they played hard. They scrapped. They have a scrappy team. We knew that coming into tonight. We knew it wouldn't be easy, but we got some things we can correct and come back ready [for Game 4]."