Buttler charged in from the long-off position and covered a good distance to make it to the edge of the circle before diving forward and grabbing a sensational low-height catch.
Prabhsimran (60 off 34 balls), who hit a breezy half-century which included seven boundaries and three maximums, added 90 runs for the opening wicket with skipper Shikhar Dhawan.
Earlier, Royals skipper Sanju Samson won the toss and put Punjab Kings into bat. Both the teams fielded an unchanged side.