When MINAMOTO no Yoritomo, the bereaved child of Yoshitomo raised his army in 1180, Sanemoto participated in the army with Motokiyo GOTO, his adopted son.
治承4年（1180年）に義朝の遺児・源頼朝が挙兵すると、養子の後藤基清とともにその麾下に参加。