Virgin Hotels Las Vegas, Las Vegas - Three division champion Vasiliy Lomachenko (15-2, 11 KOs) stopped Masayoshi Nakatani (19-2, 13 KOs) in the ninth round.
Lomachenko scored a knockdown in the fifth with a combination of punches. He battered Nakatani with punches during the ninth to drop him again for the stoppage.
For Lomachenko, it was his first bout since losing a twelve round unanimous decision to Teofimo Lopez in their lightweight unification fight last October.
Nakatani was in action back in December, when he knocked out Olympian Felix Verdejo.