NEW YORK: Light-heavyweight world champion Artur Beterbiev knocked out American rival Joe Smith Jr. inside two rounds on Saturday to add the WBO title to his WBC and IBF belts.

The unbeaten 37-year-old Canada-based Russian scored three knockdowns and had Smith in deep trouble with just under a minute remaining in round two before the fight was stopped.

Beterbiev improves to 18-0 - all by knockout - and can now set his sights on a possible unification fight against Russia’s WBA champion Dmitry Bivol for the undisputed light heavyweight crown.

“Joe is a little bit open, and it was more easy for me to get him,” Beterbiev said afterwards, before turning his attention to the prospect of a fight with Bivol.

“I’ve had two unification fights and unification fights are more interesting,” Beterbiev said.

“I prefer to unify. I want to be undisputed.”

Smith, who was reportedly taken to hospital immediately after the bout and did not speak to media, meanwhile fell to 28-4 after the fourth defeat of his career.

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The 32-year-old American underdog, who also has 22 knockouts on his record, started aggressively but was quickly overwhelmed by his hard-hitting and skilful opponent.

Beterbiev had Smith wobbling in the first round, connecting with a series of overhand rights.

He had the American on the canvas early in what was ruled a slip rather than a knockdown.

But he did not have long to wait for the first legitimate knockdown of the contest, once again a clubbing overhand right forcing Smith to take a standing count at the end of the first.

After starting the second round in similar fashion, it was only a question of how long Smith would be able to cling on.

Beterbiev scored two more knockdowns early in the round, almost sending Smith through the ropes with a flurry of vicious shots.

He then uncorked a deadly combination of left uppercuts and a right to scramble Smith’s senses further, leaving referee Harvey Dock no option but to call it off.