However, after Masamune DATE, the son of Terumune (his lawful wife was Princess Ai, the daughter of Kiyoaki TAMURA) took over as head of the family in 1584, Masamune sided with the Tamura clan and attacked Sadatsuna, one of such attacks being a clean sweep of opponents in Odemori-jo Castle; thus Sadatsuna abandoned Obama-jo Castle and escaped to Nihonmatsu (a town in Adachi District), and then relied upon the Ashina clan of Aizu Province.
しかし、1584年に輝宗の子・伊達政宗（正室は田村清顕の娘・愛姫）が家督を継ぐと、政宗は田村氏に加担して定綱を攻撃し、小手森城で撫で斬りを行うなどしたため、定綱は小浜城を放棄して二本松へ逃れ、ついで会津の蘆名氏を頼った。