The reigning world champion showed his quality against Italy's Clemente Russo, who was looking to improve on the silver medal he won at Beijing 2008.
Russo landed a right hand for the first score of the fight and moved into a 3-1 lead after one round as Usyk failed to fire.
Things changed in the second, however, Usyk initially appearing to land a knockdown with a left hook only for the referee to rule that Russo had stumbled.
There was a big exchange of blows as the second came to an end but Usyk had the better of it and took the round 7-5.
He closed out a 14-11 victory in the final round as Russo, looking to force the win, missed with a series of big hooks only to be caught by his more measured rival.