The 33 year-old, reigning WBC bantamweight champion since 2011, defeated Anselmo Moreno for the second time following a disputed decision a year ago.
This time around, ex-world title holder Moreno hit the canvas three times before eventually being stopped in the seventh by referee Daniel Van der Wiele.
Yamanaka had to pick himself up in the fourth round in order to get the job done but completely ended any argument from the Moreno camp with the win.
“This was my toughest opponent. He did knock me down, but I was able to keep going and I thought I’m going to get him with one more round,” Yamanaka said after the fight. “Moreno fought hard, so to win in this fashion is extremely satisfying. I am so happy to be a boxer.”
In the co-feature, it was more joy for the Japanese crowd as Hozumi Hasegawa became three-weight world champion at the second attempt when dethroning Hugo Ruiz of his WBC super-bantamweight belt.
An exciting battle through three quarters of the contest saw Hasegawa ahead on the scorecards, and after taking some punishment in the ninth, Ruiz failed to come out for the next session.
Hasegawa, 35, was clearly delighted to once again be a world ruler after five and half years without a title, having improved his record to 36-5 with a 16th stoppage.
“That final exchange won the fight. This is like a dream. Today was made possible by this past 5-1/2 years. Had I lost, I was planning to retire, but I was convinced I would win,” said Hasegawa.
