Times in boxing when one punch could change everything...

Pavlik v Talyor (1) If Taylor just landed one clean shot on pavlik when Kelly was dazed and stumbled across the ring after being knocked down once already in the fight, then we probably wouldn't have had a rematch since it would seem like such a convincing win because it would have been an early KO. (I know there was a rematch clause but this was for only Taylor I believe.) This in turn would of kept Taylor on the radar most likely for a Calzaghe showdown in place of other fights. Can anyone provide some examples where one punch could change it all or a if a judge gave a split decision the other way? And what chain reaction it would have caused.