Gassiev (34-2, 27 KOs) was elevated to full champion last month after Oleksandr Usyk vacated the title along with the IBF and WBC belts. Kadiru stepped only days ago to replace Tony Yoka, who withdrew from the bout on July 2 because of a back injury.

It was largely one-way traffic for Gassiev, who is The Ring’s No. 9-ranked heavyweight. The 32-year-old from Vladikavkaz, Russia, found plenty of success punching through and around Kadiru's guard. He also had success going to the body.

Kadiru (23-2, 13 KOs), who entered the bout on a nine-fight win streak, fought back in spurts, but the 29-year-old German struggled to sustain any resistance.

The beginning of the end came early in the sixth round when Gassiev landed a left hook around Kadiru’s guard that forced him to retreat along the ropes to his corner. Gassiev pulled down Kadiru’s left hand and landed three consecutive hard right hooks.

After a solid left hook to the body, Gassiv landed a right uppercut before following up with a barrage of punches, which led to Kadiru’s corner stepping onto the apron and waving the white towel to stop the fight.