Hopkins won with a 12th round technical knockout at Madison Square Garden in New York.

And by adding Trinidad's WBA belt to his own IBF and WBC titles, he became the first man in 14 years to unify the middleweight titles.

He surprised the New York City crowd by dominating the fight throughout - and was leading comfortably on all three judges' scorecards when a huge right hand to the chin put Trinidad on the canvas.

Trinidad struggled to his feet on the count of nine, but referee Steve Smoger called a halt to the action one minute and 18 seconds into the final round.

By winning the middleweight unification tournament and handing Trinidad his first professional loss, Hopkins tied the late Carlos Monzon's record of 14 consecutive title defences in the middleweight division.

The defeat was a shock to Trinidad's system, the Puerto Rican having won his previous 40 fights.

But the contest at Madison Square Garden in New York was a very one-sided affair and it would have been more of a shock had Trinidad fought back to beat Hopkins.

The victory gave Hopkins a 14-1-1 record with 10 knockouts in championship matches.

Trinidad's loss ended a run of 20 victories, 17 by knockout, in championship bouts.

Hopkins v Trinidad undercard

Earlier, Byron Mitchell retained his WBA super middleweight title despite being knocked down in the final round by opponent Manuel Siaca, in New York.

Mitchell won the contest on a points aftre dominating the middle rounds.

The American had to put up a strong guard in the final two and was dropped to the canvas with a left-right-left combination from the Puerto Rican, in the 12th.

Mitchell was up quickly and responded with a furious finish. Two of the judges gave him the fight 114-112, while the third judge made it 115-112 for Siaca, the WBA's fourth-ranked contender.

Mitchell improved to 24-1-1, with 17 wins inside the distance, while Siaca fell to 15-4, with 14 knockouts.

Cuba's Joel Casamayor retained his World Boxing Association super featherweight title, stopping American Joe Morales in the eighth round.