In 1564, Tadatsugu achieved distinguished war services by completing the exclusion of the Imagawa Clan from Mikawa Province and attacking Yoshida Castle (in Mikawa Province) (Toyohashi City, Aichi Prefecture) and was immediately selected as the lord of Yoshida Castle.
永禄7年（1564年）には、三河国から今川氏を締め出す総仕上げ・吉田城(三河国)（愛知県豊橋市）攻めで戦功を立て、そのまま、吉田城主に取り立てられた。