Hideto Asamura's seventh-inning RBI single snapped a 4-4 tie before the Seibu Lions batted around in the eighth to bury the Chiba Lotte Marines 10-4 on Friday.
The win moved the Pacific League-leading Lions five games ahead of the Fukuoka SoftBank Hawks after the defending champions lost 3-1 at home. Seibu hasn't won the PL pennant or Japan Series since 2008.
Facing lefty Kota Matsunaga (2-3) with two outs and Yuji Kaneko on second after a leadoff double, Asamura singled to left to put the hosts in front.