Kim Yong gave home team the lead eight minutes after the break before Nigerian striker Ranti Martin scoring one to inflict injury to his former club. T Lalnunpuia, who replaced Steven Dias 10 minutes before the final whistle, scored twice as the visitors were left embarrassed.
United's Eric Brown did not perform as expected by his club even as Baldeep Singh and new recruit Waheed Adekunle were hardly considered a threat for Rangdajied keeper.
Rangdajied have won thrice this season, drawn on four occasions with only East Bengal and Mohammedan Sporting emerging victorious in their Shillong outing.
"We worked hard as we improve our fitness level and we will continue to give our best in our games ahead," Rangdajied coach Herring Shangpliang said.