When the company turned to mixed martial arts, he had his first fight on January 25, 1995, facing off another debutant, Dutch fighter Hans Nijman.
After winning his next bout for via unanimous decision at an event in Amsterdam for the organization, Yamamoto faced off against legendary Brazilian jiu-jitsu specialist, Rickson Gracie at Vale Tudo Japan 1995.
However, the former professional wrestler would bounce back, defeating South African kickboxer Jan Nortje via armbar submission less than two minutes into the fight.
In his next bout at Pride Final Conflict 2003 Yamamoto fought Heath Herring and performed well against the Sambo and Muay Thai specialist but ultimately lost via rear-naked choke submission in the third round.
Early in the fight Kerr secured a double leg takedown but spiked his head into the canvas, stunning himself, which allowed Yamamoto to capitalize with ground and pound for the first round knockout win.