CLEVELAND -- The Boston Celtics couldn't hold onto a late lead, and Avery Bradley couldn't hold onto the ball. Ultimately, it didn't matter.

Bradley recovered in time to make a 3-pointer at the buzzer Friday, and the Celtics stormed out of Quicken Loans Arena with a stunning 104-103 victory over the Cleveland Cavaliers after they rallied from five points down in the final 18.6 seconds.

The Celtics blew a seven-point lead with four minutes left, but Bradley's shot against the team that swept the Celtics in the first round of the playoffs last season bailed them out.

"In the big picture, it does count as one, but it gives you a sense you're improving and getting better," Celtics coach Brad Stevens said. "For us, it would have been disappointing to lose that lead and not come out with a win. They made huge plays late in the game, but our guys stayed poised. To score five points inside eight seconds is a good deal."

The Cavs seemed to have the victory sealed when guard J.R. Smith grabbed an offensive rebound off forward LeBron James' missed 3-pointer with 22 seconds left. Guard Kyrie Irving made a pair of foul shots for a four-point lead, but Smith fouled Evan Turner while the Boston swingman was driving for a basket with four seconds left.

Turner's hoop pulled the Celtics within 103-101, but he missed the free throw, and the ball trickled out of bounds off the Cavs. It gave possession back to the Celtics with one final shot to win it.

Forward Jae Crowder inbounded to guard Isaiah Thomas, who started to drive before spinning and passing back toward Bradley. Bradley momentarily fumbled the pass but recovered in time to get the shot off with guard Iman Shumpert -- the Cavs' best perimeter defender -- standing in front of him.

"I knew it was there," Bradley said. "It's a great feeling."

James scored 30 points, including 13 in the fourth quarter, but was so upset he put in a rare postgame workout before speaking with reporters.

"It's how we lost. It hurts," James said. "It's been a while since I felt like this."

When asked if he thought the defense covered Bradley's shot well, James said, "No."

"The only thing that can beat us is a 3," he said. "It's unfortunate that's what happened."

Thomas scored 22 points and Turner had 19 points, 12 rebounds and six assists off the bench for the Celtics.

Smith scored 20 points before fouling out on the critical play that sent Turner to the line. Irving had 19 points and six assists for the Cavaliers.

"There were more than a few mental mistakes going down in those last final seconds until that buzzer went off," said Irving, who didn't appear nearly as upset as James following the loss. "It was just a few bad bounces that obviously can be corrected by us."

Forward Kevin Love's run of bad luck against the Celtics continued when he left the game late in the third quarter with a bruised thigh. Love was bumped by guard Marcus Smart under the basket with two minutes left in the quarter and dropped to the ground. He was writhing in pain on the baseline for a few moments and had to be helped to the bench before limping to the locker room.

"Probably for 10 minutes there it was a dead leg," Love said. "I don't know what it will feel like (Saturday), but I'm optimistic it's just a thigh bruise, nothing else."

Love left the game with 10 points and five rebounds, although he had eight points and four rebounds after the first quarter.

The Celtics have won three straight, while the Cavs fell to 5-3 under new coach Tyronn Lue. Cleveland, which shot just 21-for-35 from the free-throw line, lost a second game in a row. The Cavaliers' lead over the Toronto Raptors for the top spot in the East is down to 1 1/2 games.

NOTES: Boston F Kelly Olynyk made his first appearance in Cleveland since dislocating F Kevin Love's shoulder during the playoffs last season. Olynyk was roundly booed when he entered the game and whenever he touched the ball. ... Celtics F Jae Crowder did not participate in Friday's shoot-around but played through a sprained ankle. He shot 1-for-9, but his basket was a big 3-pointer in the final seconds to cut the Celtics' deficit to 101-99. ... Cavaliers G J.R. Smith was not invited to the 3-point shooting event at All-Star weekend. He has never been invited despite ranking 18th all time in 3-pointers made. F LeBron James campaigned for him to make the team last month but to no avail. "I might take the Marshawn Lynch approach on this one, so I don't get fined," Smith said. "I got a lot to say about it, but I'm not going to say anything because it's not going to help it." ... Cavaliers G Matthew Dellavedova missed his second game with a sore left hamstring. Coach Ty Lue indicated Dellavedova could miss Saturday's game against the New Orleans Pelicans as well.