The Riflemen surged ahead in the second minute of the match through striker Thoi Thoiba Singh, followed by another goal by Meikingai Kamei in the very next minute.
Assam Rifles swelled the lead in 13th minute via Akum Ao.
Hirojit Kumar (90th) was the other scorer for winning party, while striker Samson Oyeleke (82nd) produced the consolation goal for Simla Youngs.