Evander Holyfield's KO of Mike Tyson was quite surprising but Tyson did step into the punch.
It's a difficult one really because on a lot of these occasions like when David Haye got stopped by Carl Thompson the (KO masters), had punched themselves out or had been out witted.

You could almost add some of Muhammad Ali's victories to the list.

But a genuine unexpected KO by a soft punching fighter against an opponent who was not tired or mentally destroyed I am struggling to think of one.