Some good ones so far but it took a while for Cockney to get Marciano - Walcott. The perfect punch. Doesn't get much better then that. But imo...

Floyd Patterson over Ingemar Johansson. Absolutely sickening. Patterson was on the outside, lunges in, put everything he had into a left hook that connected flush and sent Johansen flying. He was knocked unconscious and all the while his leg was twitching violently. Tthe most brutal knockouts ever recorded in a heavyweight title fight imo.

Probably the most significant one punch KO too, as it made Patterson the first ever 2 time heavyweight champion.