Vitali was knocked out by Pele Reid who went 0-4 in K1 , with 2 of those by KO/TKO. Its also said he was KOed by Robin Van Roosemalen's father like others have said in this thread, but I can't find any video. Just remember Vitali was a kickboxer before he was a boxer. I think he even lied about this one and said it was from a leg kick to try to save face.
https://www.youtube.com/watch?v=9n7zExsuCRU < is Vitali vs Pele
And I don't understand why people say Tyson had a lot of punching power. Go look at some of his fights, they aren't one punch KOs and most of the time they aren't cold. I know Mike Tyson wanted to fight Bob Sapp and if it had happened at that time I would give it to Sapp atleast 9 times out of 10. Sapp was a beast when he actually tried and have some devasting kicks when he actually threw them and he could take a beating unlike any other.
Boxers don't have magical chins or punching power like a lot of people say they do, they just have movement that suits boxing. I'd say Francisco Filho may have been the hardest puncher in all combat sports in the early 2000s.
Jarrell "Big Baby" Miller who lost to an old, worn out Cro Cop in '14 is now 12-0-1 in boxing and ranked 63 in the world by the IBO
http://www.iboboxing.com/rankings/heavy.html for proof.