Terence Crawford punished Errol Spence on the way to a ninth-round technical knockout to claim the undisputed welterweight world title in Las Vegas on Saturday.

Unbeaten Crawford had knocked down Spence three times and had his previously unbeaten foe staggering under a hail of blows when referee Harvey Dock called a halt at 2:32 of the ninth round.

Crawford added Spence's World Boxing Association, World Boxing Council and International Boxing Federation titles to his own World Boxing Organization crown.

Crawford became the first undisputed welterweight world champion of boxing's four-belt era, which began in 2004.

A former lightweight and undisputed light welterweight world champion, he became the first man to win all the belts in two weight divisions.

"Tonight, I believe I showed how great I am," said Crawford, who improved to 40-0 with 31 knockouts, taking his string of stoppages to 11 fights.

That includes all eight of his fights at welterweight.

It was a stunningly dominant performance against an opponent that had come into the bout at 28-0 with 22 knockouts but fell to 28-1.

Spence made the running in the opening round, but Crawford began to let his hands go in the second, punishing Spence with his piston-like jab and dropping him at the end of the round.

Spence was still moving forward in round three, but the power and accuracy of Crawford's counter punches was devastating.

Crawford landed a series of hard punches in the fourth, including a left that rattled him and the ring doctor took a close look at Spence at the end of the round.

It was more of the same in the sixth, and in the seventh Crawford had Spence down again with a right uppercut, then again with a blow to the chin in the waning seconds.

Crawford was landing at will as Spence struggled to stay on his feet when the referee brought it to a close, sparking a celebration for Crawford who then had an embrace and words of encouragement for his beaten rival.

bb/sev