In June 2001, Kosaka fought luta livre specialist Renato Sobral, who had defeated Kosaka's countrymen Kiyoshi Tamura and Hiromitsu Kanehara. Sobral controlled the stand-up segments via wrestling and knee strikes, while Kosaka worked from the bottom and pursued submissions. Action increased at the second round, where Kohsaka and Sobral exchanged positions and reversals, but the Brazilian kept the dominance and it forced Kosaka to resort to sacrifice techniques like kani basami and flying kneebars. Victory by majority decision was given to Sobral.