The 32-21 win enabled the defending champions to finish third with 25 points.
Rishank and captain Rakesh Kumar, who remained on court for the full duration of the match, will be more than satisfied for having kept the team afloat in the absence of four of their stars.
The win also helped U Mumba to maintain their unbeaten record against their rivals.
Pawan Kumar's couple had put the U Mumba side ahead at 14-10 but the losers caught up soon. But Rishank's decisive raids made it 20-16 in the 30th minute. U Mumba then started giving bonus points to Nitin but at the same time focused on their own strategy to canter ahead 23-16 by the 32nd minute.