Oleksandr Usyk stopped Chazz Witherspoon in seven rounds on his heavyweight debut.
Witherspoon retired after Usyk landed a devastating barrage of punches in the seventh, having gradually cranked up the pressure during the fight.
Usyk outclassed Witherspoon, landing 139 punches to his opponent's 21, with the Ukrainian hitting the target with 70% of his power shots.
Ukrainian Usyk has taken 12 months to build into the bigger weight after he stopped Tony Bellew last year to become the undisputed cruiserweight world champion.
After gauging time and distance in a cagey opening first round, Usyk landed his first straight lefts in the second, showing superior footwork to his heavier opponent.
The Ukrainian started to turn up the heat in the third, landing more punches and momentarily forcing Witherspoon back to the ropes.
He pinned Witherspoon in the corner in the fourth as he unleashed some fast hands on him, but was still searching for a way to hurt his opponent.
Usyk started to pepper Witherspoon with punches in the fifth, landing a couple of head shots, and had his opponent in the corner again at the bell.
The referee had a look in the sixth as Usyk pinned the American in the corner again and unleashed a combination.
But the fight was allowed to continue into the seventh, and Usyk got his hands away with a devastating barrage. Witherspoon tried to respond and made it to the end of the round before retiring.
Usyk had initially been due to face Tyrone Spong on his debut but an adverse finding in a drug test saw him replaced by Witherspoon.
