The Thunder's Kendrick Perkins was given a basket on the play with 1:05 to go, which handed Oklahoma City a 102-101 lead en route to Sunday's 107-103 victory over the Nuggets in Game 1 of their Western Conference quarterfinal series.
Referees ruled Perkins had legally tapped in a shot by Russell Westbrook from the right side. The ball rattled around the rim while Perkins and other Thunder teammates leaped for a possible tip-in.
Replays, however, appeared to show Perkins interfered with the net and the ball was in the cylinder when he tapped it, which would disallow the basket under offensive goaltending rules.
The league admitted Monday Perkins' score shouldn't have counted.
"Although a player is permitted to touch the net while the ball is in the cylinder above the rim, Perkins also touched the ball while it was still in the cylinder which is a violation and constitutes goaltending," the NBA said in a statement.
The finding has no affect on the game's final score, however.