How was M.Tyson able to knock out so many strong opponents quickly?

There was no one in boxing history who had the tools Mike Tyson had: speed, power, accuracy, chin, defense and the intimidation factor. He was short and stout...AND fast.

I remember Vinny Pazienza stating that Mike was faster than him when they both worked under Kevin Rooney. Imagine that, a bull of a heavyweight being faster than a man 60 - 70 lbs. lighter. And Pazienza was quite fast himself.

 

Another factor was Tyson's opponents assumed the best way to deal with a smaller pressure fighter was to fight on the backfoot and keep him at range which was exactly what you should not do against Tyson, if he's coming forward with momentum and you back off you're finished.
As Holyfield, Douglas and to a lesser extent Ruddock demonstrated if you stand your ground, fight back in an intelligent manner and smother Tyson up close you can cause Mike real problems.

 

Most of those guys were pure boxers used to chess matches. Few heavyweights of the 80’s went out to blast someone out quick. I think they were all fighting at a different tempo than Tyson. They were looking to jab and outsmart. He went out to overwhelm everybody.

 

Speed,power, intent and uniqueness.

Tyson's combination of speed, power and aggressiveness was absurd, particularly early. He also came at people in different ways with different assets to everyone else. He was unique and took the division by storm. None of his opponents had seen anything like him and were often overwhelmed. He was something new to everyone. As one poster pointed out early most thought it best to back off and box but this was exactly what Tyson's style thrived on.