CLEVELAND – If the Boston Celtics and Cleveland Cavaliers were to play 50 games, Marcus Smart would probably outplay LeBron James one time.

Game 3 on Sunday was that one time. Smart played the game of his life, Avery Bradley hit the shot of his life, and a 111-108 victory has given Celtics life in the Eastern Conference finals.

The Celtics were playing on the road without their All-Star point guard, just 48 hours after losing by 44 points at home. Midway through the third quarter, they were down 21 to an opponent that was looking unstoppable, less than 19 minutes from a 3-0 deficit that has never been overcome in NBA history.

But Celtics coach Brad Stevens liked what he saw a lot more than he did two nights earlier.

“We were playing way better,” he said afterward. “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.”

His team proved him right. The Celtics came all the way back, were the better team down the stretch, and Bradley’s 3-pointer with 0.1 second left was the difference. If it wasn’t the turning point in the series, it was at least an exhibition in resilience and the first loss for the two teams looking to meet in The Finals for the third straight time.

We’ll surely get that Cavs-Warriors three-match, but the Celtics are too stubborn to concede it.

“We’ve got guys that have chips on their shoulders,” Stevens said. “A lot of these guys have been overlooked and this is their first opportunity to really play a meaningful role.”

Smart is at the top of that list. And with Thomas out, Sunday was his first opportunity to start a playoff game this year. He’s always been counted on to play hard and beat everybody else on the floor to loose balls. But, to put it nicely, his shooting is less reliable than his hustle. There were 135 players who attempted at least 200 3-pointers this season. Smart was the worst shooter of the bunch, making just 28.8 percent of his 3s.

But the ball bounces a little differently every night. It bounced off the rim five times and also off the backboard before Bradley’s game-winner fell through the net. After shooting 31 percent from 3-point range in Games 1 and 2, the Celtics were 18-for-40 (45 percent) from beyond the arc on Sunday.

Smart, the worst high-volume 3-point shooter in the regular season, was 7-for-10, outscoring James 27-11. The 11 were the fewest James has scored in 107 career home playoff games. The Celtics did a better job defensively, with Jae Crowder recovering from screens to keep Kelly Olynyk from getting isolated with the best player in the world as much as he did in Games 1 and 2.

Smart’s 27 points, meanwhile, were a career-high, regular season or playoffs.

“We can talk about his shooting all year long,” Stevens said of Smart, “but you know when it’s in a big moment, that kid is going to rise to the occasion. He just always has. That’s one of the reasons why if he goes through a funk at some time in March, shoot yourself out of it, and we believe in you, and let it fly. Because in this moment when we needed him the most, he made huge shots.”

Three of them came in a 14-3 run that quickly cut that 21-point deficit to 10. Two more 3s came in the fourth quarter, the second a step-back in the face of J.R. Smith that tied the game at 95 with a little less than six minutes to go. It was a shot that a 29-percent 3-point shooter should not have in his arsenal. But maybe Smart isn’t aware of how bad a shooter he is.

“One of the things about Marcus is he’s going to play regardless of the score,” Stevens said. “He’s going to compete, and sometimes he’ll try to hit home runs.”

Sometimes, he succeeds. And a few possessions after Smart made a Stephen Curry play, he made a Marcus Smart play, grabbing an offensive board and feeding Al Horford for a 3 that gave the Celtics the lead.

Smart played all but 37 seconds of the second half and Stevens had the ball in his hands all night. On the final possession, Smart had the attention of James, leaving Smith and Iman Shumpert to get mixed up on an off-ball action that led to Bradley’s game-winner.

“We were able to stick together at the end of the game and make some big plays,” Bradley said. “I think it started with Marcus Smart, how poised he was at the end of the game. He was able to get us in our sets and make the right play.”

The Celtics don’t have Isaiah Thomas for the rest of this series, but they do have Marcus Smart. It’s not clear that he’s any more a point guard than he is a shooter. But he’s a gamer and even if the Celtics can’t count on the shooting for the rest of this series, they can count on the hustle.

“I just kept telling myself, you have nothing to lose, just go out there and play,” he said. “You’ve been working hard throughout this whole year on your game. Just let it flow and let it show.”

John Schuhmann is a staff writer for NBA.com. You can e-mail him here and follow him on Twitter.

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