Fighting Network RINGS A high school
judoka, Yamamoto made his professional debut on the then puroresu promotion
Fighting Network RINGS in 1991 against
Masayuki Naruse, who was also making his debut. 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. Yamamoto lost the bout when he was knocked out only 43 seconds into the fight. 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. Yamamoto gave the undefeated fighter arguably the most difficult fight of his career, but the former professional wrestler ultimately lost via
rear-naked choke at 3:49 of the third round, the referee having stepped in when Yamamoto refused to tap out. This would be the only fight that Gracie ever had that didn't end with him winning in the first round. The fight with Gracie elevated Yamamoto's status. In his next bout, he won via neck crank submission before losing via
keylock submission to his teacher
Akira Maeda and then to
Ricardo Morais, who knocked out Yamamoto 46 seconds into the fight. In his next bout, Yamamoto faced
David Khakhaleishvili, an
Olympic Gold Medalist in
judo. Yamamoto defeated the
Georgia fighter via
TKO 40 seconds into the fight before competing in the
Rings - Battle Dimensions Tournament 1996 Final. Yamamoto won his fight in the quarter-finals of the tournament and then lost in his semi-finals match against
Kiyoshi Tamura. Yamamoto then went 7-7-1 in his next 15 fights with wins over
Valentijn Overeem,
Joop Kasteel, and
Tsuyoshi Kosaka before being invited to compete in
PRIDE.
PRIDE Yamamoto made his PRIDE debut at
Pride 16 on September 24, 2001 against Brazilian
Assuério Silva and was dominated, losing only 11 seconds into the fight via TKO. 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 bouts he was knocked out by former
NFL lineman Bob Sapp and then lost via unanimous decision to
Guy Mezger before picking up his next win against
Alexander Otsuka after Otsuka injured his leg in the second round. 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. In his next bout the 13-16-1 Yamamoto faced two-time UFC Heavyweight Tournament Champion
Mark Kerr. 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. Yamamoto's next appearance for the organization was at
Pride Bushido 2 against future
2006 Pride World Grand Prix Champion Mirko Cro Cop. Yamamoto lost the bout via TKO 2:12 into the first round. Yamamoto fought once more the organization at
Pride Bushido 3 against
Choi Mu-Bae and lost via unanimous decision.
Post-PRIDE After PRIDE, Yamamoto fought for
K-1 Hero's, and DEEP, but has not won since his TKO win over
Mark Kerr, losing his last nine fights. ==Mixed martial arts record==