Australia's Jeff Horn has failed to retain his WBO welterweight belt, losing to American Terence Crawford by technical knockout in Las Vegas.

The American dominated the contest from start to finish and had Horn unsteady on his feet after some big hits in the eighth round, before getting the knock down in the ninth.

Referee Robert Byrd called off the fight two minutes and 33 seconds into the ninth round, giving Crawford the welterweight title.

Sorry, this video has expired Jeff Horn beaten by Terence Crawford by TKO

Horn, from Brisbane, said he was disappointed to lose to Crawford, but that the loss would not be a major setback in his career.

"I'm disappointed but I'm not hurt at all, these things happen. It's my first loss as a professional, I can keep going, I can rebuild," Horn said.

"He was a tricky boxer out there, he's hard to tag. He managed to clip me … good on him.

"I could have faked it a bit more, kept him guessing."

Referee just acting in my interests, says Horn

The referee had spoken to the Australian after appearing shaky at the end of the eighth round, and Horn said the adjudicator was simply acting in his interest, as much as he would have liked the bout to go on.

"I was slightly off balance on one of my feet, I wish I could keep going to the end," Horn said.

"The ref said to me he's got my interest at heart. I'm sure my wife Jo is happy anyway."

Terence Crawford defeated Jeff Horn by technical knockout in the ninth round. ( AP: John Locher )

The victory ensures Crawford remains undefeated in his 33 professional fights, including 24 wins by knockout.

He has become just the sixth fighter in history to win world titles at lightweight, light welterweight and welterweight.

Crawford said he now wanted to fight the other champions at welterweight, and called on promoter Bob Arum to "make it happen".

He said had proved critics wrong by dominating the fight against Horn.

"Y'all kept telling me how strong he is, but you didn't give me enough credit so I had to go in and show y'all," he said.

It was the first loss of Horn's career, who had become world champion after a shock defeat over Filipino great Manny Pacquiao at Lang Park in July 2017.

The Australian's record now stands at 18 wins (12 by knockout), one draw and a loss.