There was a lead right uppercut thrown by Marvin Hagler once that turned Willie Warren into Willie Wonker, but surprisingly he got up and lasted a little while longer. He was only a short fighter so his head got scooped right up like ice cream.
A great knockout but not exactly what the thread author asked for. A better example would be Foster's one-two that jolted Finnegan to the floor (not the last one).
Bonecrusher Smith knocking down Ruddock was bad. Ruddock went down hard, like a sack of crap really. Of course he got up, and won.
Brutal knockdown its a testament to Larry Holmes that he got up and won. Holmes is one of the most overlooked heavies in history, and its a shame.