Masamitsu was appointed Kotaigogu gon no suke (provisional assistant master of the Empress Dowager's household), when the Crown Prince was enthroned to become Emperor Ichijo and the Emperor's mother FUJIWARA no Senshi became Kotaigo (Empress Dowager); this shows that he was recognized as one of the Kaneie's close retainers.
さらに寛和2年（986年）にその東宮が一条天皇として即位して、母藤原詮子が皇太后となると、皇太后宮権亮に就任し、兼家の近臣として認められている様子がうかがえる。