To prevent Futamata-jo Castle from being taken by the Takeda side, Ieyasu conducted reconnaissance in force to know the movements of Takeda's troops, but encountered Takeda's troops and was defeated at Hitokotozaka (the Battle of Hitokotozaka).
二俣城を取られることを避けたい家康が、ひとまず武田軍の動向を探るために威力偵察に出たところを武田軍と遭遇し、一言坂で敗走する（一言坂の戦い）。