The Utsunomiya Brex overcame SeaHorses Mikawa newcomer Davante Gardner's game-high 40 points to earn a 92-86 series-opening home win on Saturday.
Ryan Rossiter paced the Brex (4-2) with 20 points, 14 rebounds, seven assists and three steals.
Five teammates also scored in double figures: Makoto Hiejima, Yusuke Endo and Hironori Watanabe (13 points apiece), Seiji Ikaruga (12) and Kosuke Hashimoto (11).