Boland produced a spirited second half performance which gave the homeside a scare but in the end, the Kings had done enough in the first half to secure the all-important victory.
The quarter-finals will be a cross-section playoff with the finals positions in both sections to be decided on Saturday.
The Kings, who only registered a penalty off the boot of flyhalf Justin van Breda in the second half, were far from convincing as Boland came running at them in the second half.
Flank Franzel September brought the visitors back into contention when he scored a try far out in the 43rd minute. Flyhalf Elgar Watts kicked the conversion to reduce the deficit to nine points.
Van Staden kicked his penalty shortly after September's try but when Boland replacement Jonathan Francke crashed over for a converted try with only four minutes remaining, there were some nervous moments for the homeside.
The Kings managed to hang on but will be disappointed that they were not able to capitalise on their first half dominance and push through for a bonus point try.
EP opened the scoring in the sixth minute when flyhalf Justin van Staden slotted a penalty after Boland were penalised at the breakdown.
Watts levelled matters with a penalty of his own four minutes later but from then on the homeside dominated the majority of the remainder of the first half.
Former Springbok wing Jongi Nokwe took a final pass to score the Kings' first try after 13 minutes.
Centre Scott van Breda extended EP's lead when he forced his way over for the team's second score. This time, Van Staden slotted the conversion and also added two quick penalties within miniutes of each other to thrust the Kings into a 21-3 lead.
All the while Boland were try to crack a resolute Kings defence by spreading the ball when the opportunity presented itself. It did not help matters that they lost captain and former Bok scrumhalf Bolla Conradie midway through the first half due to injury.
They were eventually rewarded for the persistance when centre Siviwe Magaba scored after numerous phases. Watts converted to make the score 21-10.
But EP had the final say in the first half when Marcello Sampson scored their third try.
Scorers:
EP:
Tries: Jongi Nokwe, Scott van Breda, Marcello Sampson; Conversions: Justin van Staden (1); Penalties Justin van Staden (4).
Boland:
Tries: Siviwe Magaba, Franzel September, Jerry Sifoko; Conversions: Elgar Watts (3); Penalties: Elgar Watts.