In 1467, when the Onin War erupted, Tsunemoto belonged to the eastern army led by Katsumoto HOSOKAWA and was engaged in fierce and mortal combat with troops led by Sozen YAMANA of the western army inside the capital, earning great renown for his bravery across all parts of the country.
1467年、応仁の乱が発生すると、細川勝元率いる東軍に属し、西軍の山名宗全の軍と洛中にて壮絶な死闘を展開し、その勇名を全国に轟かせた。