Danny Williams capped the best night of his boxing career by proposing to his girlfriend Zoe Browne after recording a shock fourth-round knockout over former world champion Mike Tyson on Friday.

The little-known British heavyweight and his partner have been together for 13 years and have two daughters.

Williams, 31, said he did not even know his family were in town for the fight and, after he saw them from the ring, he proposed and Zoe accepted.

"I've never had a bigger moment than this," Williams told reporters.

Perhaps the only person who believed the 9-1 underdog could defeat the former "baddest man on the planet" was Williams himself.

Executing a perfect strategy that badly tired the 38-year-old American, Williams stunned the boxing world by battering Tyson into submission.

"I was sure of myself all along. I trained for this kind of fight," Williams said.

ALI'S HOMETOWN

The kind of fight Williams planned was to survive a first-round onslaught by Tyson and then wear his opponent down, and that was exactly what happened in the hometown of Muhammad Ali.

"Tyson always tries to jump out at the start," Williams said. "The first few rounds are my worst.

"He hurt me for a few seconds in the first. He gave me a good shot but the key is getting one back on him."

Tyson, in his first fight for 17 months, was ahead on all three scorecards after three rounds but the contest ended with Williams delivering a flurry of punches that sent the American sprawling into the ropes late in the fourth.

Laying back on the ropes with blood streaming down his face from an earlier cut above his eye, it was clear the fight was over for Tyson.

"He (Williams) showed great heart, we saw good things from him," Tyson's trainer Freddie Roach said.

"I was very surprised he (Williams) fired back hard."

Now Tyson's career looks in jeopardy and he must convince a sceptical public that he still has what it takes to again be a heavyweight contender.

Williams, though, appears to have a bright new future ahead.

"I'm going to chill with my family, look for a world title shot or a rematch with Mike," said the Briton.