Improbable doesn’t begin to describe it.

The Celtics trailed the Cavaliers by four points with seven seconds left — and they managed to pull a 104-103 rabbit out of their hat when Avery Bradley stuck a 3-pointer from the left corner at the buzzer.

“It was the perfect storm. Things just went well for them down the stretch,” said Cavs coach Tyronn Lue, making an early submission for understatement of the year.

The Bostonians had trailed by nine in the last quarter. Then they led by seven. Then things got really crazy.

“If you play this game, you should believe you’re going to win until the horn goes off,” said Bradley.

Even if that belief defies logic apparently.

The Celtics were down by five points after Kyrie Irving made two free throws with 18.6 seconds left. Jae Crowder, whose right ankle was noticeably restricting him, then picked an opportune time to shake off eight misses in as many attempts and drill a trey from the left corner.

Irving was fouled intentionally and hit two more from the line at 7.5 for a 103-99 advantage. The Cavaliers would lose without ever possessing the ball again.

Evan Turner was fouled as he scored on a drive, but he missed the free throw. Marcus Smart outfought Timofey Mozgov and tipped the ball off LeBron James’ leg with 4.1 on the clock.