The career of 43-year-old future Hall of Famer Nonito Donaire hangs in the balance after his second consecutive defeat.
Donaire was dropped in round seven from a straight left and stopped after 1:12 of the eighth in Japan by the now 10- (9 KOs) Riku Masuda.
Donaire had his moments, although he suffered a cut from a fifth round clash of heads, the sixth was a shootout but ultimately Donaire's corner surrendered the Filipino great, who is now 43-10 (28 KOs).
Masuda, a Japanese southpaw fighting out of Tokyo, topped the Teiken Promotions bill at the Yokohama Buntai, Yokohama.
Donaire suffered a split decision defeat to Seiya Tsutsumi in December.
Earlier in the show, Anthony Olascuaga scored a ninth-round stoppage of Jukiya Limura to defend his WBO flyweight title.
Olascuaga dropped his man with a big left hook in the seventh and Iimura was fortunate to make it to the bell after the champion followed in.
But the challenger continued to take a beating the rest of the way before it was stopped.
Knockout CP Freshmart lost a unanimous eight-round technical decision to Shokichi Iwata for the WBC title at light-flyweight. Iwata is now a two-time champion and the Thai was withdrawn having taken a thick cut over his left eye.
