Ryuya Yamanaka, 16-2-(5), retained his WBO minimumweight title by scoring an eighth round retirement victory over Mexican Moises Calleros, 28-8-1-(16), in Kobe, Japan on Sunday.
Yamanaka was leading on three judges cards by 80-72 twice and 78-74 when Calleros was retired at the end of the eighth session.
Yamanaka was faster and controlled the pace better than Calleros, who did have some success in the third and fourth rounds.