Tatsuya Fukuhara defeated top-ranked Mexican Moises Calleros to become the WBO minimumweight interim champion on Sunday.
Second-ranked Fukuhara deployed left-handed body blows to good effect and outfought his opponent to score a 2-1 decision at Matsushima All Round Center.
"It was a tough fight to be honest and I won thanks to (the support I got from) everyone," said Fukuhara. "But I am not at the level of a world champion yet and I would like to practice more."
Fukuhara improved his record to 19 wins, including seven knockouts, against four losses and six draws. Calleros dropped to 25 (14 KOs), seven defeats and one draw.
The interim title fight went ahead as the legitimate champ Katsunari Takayama is injured.
Fukuhara must fight Takayama in order to unify the title once the latter has recovered.