Oleksandr Usyk of Ukraine retained his world heavyweight titles with a ninth-round knockout of Britain's Daniel Dubois in Wroclaw, Poland on Saturday.

Victory meant Usyk kept hold of the World Boxing Association, World Boxing Organisation and International Boxing Federation belts.

It also extended his perfect professional record to 21 wins from 21 bouts.

Dubois, however, claimed he had been "cheated" out of victory after referee Luis Pabon ruled he had struck Usyk with a low blow in the fifth round, which led to a lengthy delay.

But former World Boxing Council super-middleweight champion Richie Woodhall, commentating at ringside, described his fellow Briton's punch as a "borderline shot".

Usyk recovered to drop Dubois down on one knee in the eighth round after landing with several punches to the head.

Dubois just beat the count before the bell sounded for the end of the round.

But the fight was all over in the next, with Usyk sending Dubois onto the canvas.

This time the challenger was unable to get back to his feet before the referee counted to 10.

"I feel good. I am grateful for my team, my family, my children. I love you," Usyk told TNT Sports.

"I'm grateful for my country and the Ukrainian army. Thank you so much."