But the Leopards gained a crucial bonus point and will continue in the competition as the fourth-placed team into the semifinals.
Van der Walt, who went on several barnstorming runs through the game, scored the crucial try in the 47th minute to give the Kings a vital 23-13 cushion in a hard-fought game.
The Leopards piled on the pressure in the final quarter and it told when referee Tiaan Jonker ran around under the poles and awarded them a penalty try, with flyhalf Andre Pretorius kicking the conversion to close the gap to 20-23.
And to make matters worse for the Kings, replacement lock Darron Nell was yellow-carded for the offence that led to the penalty try.
But the log-topping Eastern Province side showed tremendous courage and determination in defence as they held off the Leopards to secure their 12th win and an unbeaten run into the semifinals.
The Leopards, playing for a semifinal place in front of their home crowd, came out firing and gave the Kings a torrid opening quarter and led 10-0 after 25 minutes.
Pretorius kicked a penalty and converted Edgar Marutlulle’s try as the hooker showed good pace and strength to barge over.
Up until then, the competition favourites had been all barks but they showed their bite through flyhalf Wesley Dunlop who scored 13 points in six minutes with two penalties and a try which he converted.
The Leopards had the last say in the first half with a Pretorius penalty, before Dunlop started the dramatic second half with a penalty to stretch the visitors lead to 16-13 before Van der Walt’s moment of glory.
PROFERT LEOPARDS – Tries: Edgar Marutlulle, penalty try. Conversions: Andre Pretorius (2). Penalties: Pretorius (2).
EP KINGS – Tries: Wesley Dunlop, Wimpie van der Walt. Conversions: Dunlop (2). Penalties: Dunlop (3).