When in March or April, 940, an imperial edict was issued to hunt down and kill Masakado who pretended to be the "New Emperor," Tamenori joined the imperial army as a commander and succeeded to defeat Masakado in cooperation with Sadamori and FUJIWARA no Hidesato, rescuing his father Korechika who had previously been raided and detained by Masakado.
天慶3年2月（940年3月～4月）、「新皇」を僭称した将門の追討に官軍大将の一人として貞盛・藤原秀郷と協力して将門と戦い征伐に成功し、先に将門に襲撃され抑留されていた父の維幾を救援した。