Oh definitely Michael Spinks
here’s the thing, Michael Spinks undefeated light heavyweight world champion, moves up to heavyweight, gives Larry Holmes his first ever professional loss, controversially beats him in the rematch and knocks Gerry Cooney out in the 5th round who is one of the hardest punchers of all time and who was considered the man who would upset Holmes first (for example Cus D’amato believed that Cooney had every attribute to pull the upset against Holmes), but it turns out that the first man who upset Holmes was Spinks, by beating Holmes Spinks proved his outboxing skills and by beating Cooney he proved that he could take on a hard puncher, at that time realistically Spinks would either pull the upset or would give Tyson a very tough fight
it turned out that Tyson knocked him out in 91 seconds and was his easiest and shortest Championship fight ever
