CLEVELAND >> Leprechauns are imaginary. Celtic pride is very real.

Avery Bradley’s 3-pointer danced on the rim and dropped with less than a second left and Boston, blown out in the first two games of the Eastern Conference finals and playing without star Isaiah Thomas, stunned the Cleveland Cavaliers 111-108 tonight in Game 3 to end the champions’ 13-game postseason winning streak.

Bradley’s shot from the left wing — off a play designed by coach Brad Stevens — bounced on the rim four times before going down. It capped a furious, focused comeback by the Celtics, who trailed by 21 in the third quarter before rallying to tighten up a series that appeared to be over.

“Wide-open look,” Bradley said. “Al (Horford) did a great job of getting me open and Marcus (Smart) made a great pass and I was able to knock down the shot.”

Smart, who started in place of Thomas, made seven 3-pointers and scored 27 points, and Bradley had 20 for the Celtics, who were given little chance after losing by 44 in Game 2 and then losing Thomas for the rest of the postseason because of a hip injury.

“Everybody had to step up their game tonight especially with one of our brothers down,” Smart said. “Our love and support goes out to Isaiah. We wish he could be here but we understand. We just kept fighting. Everybody did their part.”

Kyrie Irving scored 29 points, and Kevin Love had 28 for Cleveland. The Cavaliers dropped to 10-1 in the postseason with their first loss since Game 4 of last year’s Finals.

Game 4 is Tuesday night in Cleveland.

LeBron James had one of the worst games of his postseason career, finishing with 11 points and six turnovers.

“I didn’t have it,” said James. “You let a team like that grab momentum you almost knew a shot like that was going in.”

Still, the Cavs were in control leading 77-56 in the third quarter after making 14 3-pointers in the first half. But Cleveland got complacent, Smart got hot and the Celtics, who arrived at Quicken Loans Arena on Sunday morning for their shootaround without Thomas and looking somewhat defeated, never gave up.

“We decided were going to go out and play hard, swinging.” Bradley said. “We never counted ourselves out.”

The Celtics caught the Cavs at 95-all on Smart’s 3-pointer and then matched the James and Co. basket for basket in the final minutes in one of the most entertaining games of what has been a mostly boring postseason.

Boston’s Jonas Jerebko’s baseline jumper put the Celtics ahead 108-106 with 30 seconds left before Irving scored on a drive to tie it with 10.7 seconds left.

Following a timeout, the Celtics perfectly executed a play drawn up by Stevens and worked the ball to Bradley, who found himself open and then calmly knocked down a shot that goes straight into Celtics lore.

For Cleveland, the loss was a wake-up call on their march toward a possible third straight Finals and a seemingly inevitable rematch with Golden State. The Cavs had been playing a glorified game of H.O.R.S.E. with the Warriors, who are undefeated and can complete a sweep of San Antonio on Monday night.

The Cavs hadn’t lost since Game 4 of last year’s Finals, and they came in tied with the 1988-89 Los Angeles “Showtime” Lakers for the longest winning streak in postseason history.

With Thomas back home, the Celtics could be forgiven for feeling down after Thomas, their inspirational leader was shut down with a hip injury he first sustained in March.

However, Stevens liked his team’s energy leading up to tipoff and felt confident they would play hard.

“Our guys are itching to play,” he said. “Obviously, we’re here for a reason, and we’ve got tough-minded, competitive guys who have largely been guys that have had to really earn their way up in this league.”