Tyson vs. Douglas (1990)

Buster Douglas's tenth-round knockout of Mike Tyson in Tokyo remains the biggest upset in boxing history, with Douglas entering as a 42-to-1 underdog. He overcame a knockdown in the eighth round to land a devastating uppercut-left hook combination that ended Tyson's undefeated reign. This victory outperforms the average heavyweight championship upset in historical shock value, as no other match has seen such severe betting odds overcome.