Usyk came forward in the first round but was beaten to the punch by Russo, who waited on the back foot before picking his shots.
It was a much better second round from the Ukrainian, who battled back from 3-1 down to level the scores after two rounds.
The final three minutes were nip and tuck as the two fighters exchanged a number of blows.
Both men looked tired as the seconds ticked away, but it was Usyk who produced a strong finish.
In the end, the judges sided with the Ukrainian, awarding him a 14-11 decision.