Shakur Stevenson dominated Teofimo Lopez over 12 rounds at Madison Square Garden to claim a fourth world title.
Judges scored the junior welterweight bout 119-110 across the board.
After the loss, Lopez praised Stevenson but confused fans with comments apologising for slavery.
The remarks sparked mixed reactions, with some applauding his humility and others questioning his condition.
The fight headlined a major boxing event backed by Turki Alalshikh.
