I want to include Game 5 of the 2004 NBA Finals, but that was a multiple-game disaster that derailed a franchise.
OKC losing Game 7 against GS after blowing the 3-1 lead certainly ranks up there.
Blazers blowing Game 7 vs the Lakers.
And I'm cheating with this answer as they won the game, but a singular game in NBA history that didn't involve an on-court injury possibly changing at least parts of the course of the league?
Pistons won it all that year. And Indy was, at least IMO, a better team. With a YOUNG team (outside of Reggie.)
LMAO!!!
If not for the Bulls, Toronto would have to be the funniest team in the league.