With the Celtics and Milwaukee Bucks tied at 107 apiece in the final minutes of play, Smart drew a charge on Antetokounmpo, which would've fouled him out of the game.
However, officials overturned the call upon review, and Smart wasn't pleased with their explanation.
"The excuse was I was late on the charge," Smart said postgame. "They said the replay center said that I was late and it was a block. Quite frankly, I think we all know what that was about: Giannis' sixth foul and they didn't want to get him out. Let's just call that spade a spade. And that's just what it is."
Antetokounmpo's basket counted as a result of Smart's blocking foul, and he completed the 3-point play at the free-throw line to put the Bucks up for good.
Milwaukee can clinch the Eastern Conference's top seed for the second season with another victory. Boston fell 3 1/2 games back of the Toronto Raptors for the No. 2 seed in the East.