In an explosive showdown described by noted Japanese boxingman Joe Koizumi as Japan's "Fight of the Month", Castañares, the reigning World Boxing Foundation (WBF) super lightweight champion, sneaked in a wicked right cross that sent Yamamoto down on the canvass in the third round.
At that time, Yamamoto was already bleeding from the nostrils and Castañares from the mouth.
Yamamoto hit back in the fourth round, landing a solid right that staggered Castañares. The two protagonists were locked up in a fierce exchange of telling blows in the fifth and sixth rounds.
In the seventh, Yamamoto let loose a crackling right counter punch that flattened Castañares for good. The Cebuano boxer got up with rubbery legs, raising himself up and down while the referee completing the count. The official time was 2:58 of the seventh round.
Yamamoto, who improved his win-loss-draw record to 10-2-3 now spiked with 8KOs, is hoping to challenge Oriental and Pacific Boxing Federation (OPBF) jr welterweight champion Jungbum Kim next year.
Castañares, on the other hand, fell to 17-4-2 with 13KOs as his Japan jinx continues. It was the third straight time that Castañares, once admired for his non-stop fighting style and big heart, losy by knockout in Japan.
In his attempt to seize the OPBF title, Castañares was stopped by Masakazu Satake in the eighth round on April 26, 2003 in Tokyo, Japan. In his second trip to the Land of the Rising Sun three months later, he was decked by Venezuelan Richard Reyna in the second round also in Tokyo.
Castañares last two fights in Japan were all against Yamamoto that both ended in a draw.