5. Leon Spinks WS15 Muhammad Ali. February 1978, Las Vegas.
Muhammad Ali was badly out of shape and nearing the end of his career when he met seven-fight novice Spinks. Taking advantage, a relentless and fearless Spinks pounded on a lazy defending champion, refusing to fall for Ali’s famous Rope-a-Dope tricks. Spinks was almost as big a betting underdog as Buster Douglas would be some 12 years later against Mike Tyson; with only one betting outlet in Las Vegas taking any bets on the fight. Of course, an in-shape Ali got his revenge later the same year, but Spinks’ win remains special.
Fury beat an even older defending champion than Spinks did in dethroning a 39-year-old Klitschko. However, Klitschko was in far better physical condition than Ali was. Can Fury go one better than Spinks and win the rematch?