WP rain in four tries to two on a cool afternoon to extend their unbeaten run to six matches and at the same time book a quarterfinal place at Newlands.
They now head the south section log on 27 points and, with one round to play, cannot be caught by the second-placed Sharks (21) and joint third-placed Pampas XV, EP Kings and Kavaliers, who all have 20 points.
WP did not have matters all their own way. After dominating the scoring in the first half to lead 14-0 at the break, they managed to go further ahead when scrumhalf and vice-captain rushed over for a score soon after the restart which was converted by flyhalf Kurt Coleman.
But SWD had been tenacious all afternoon and bounced back in the 53rd minute with a try through fullback Deroy Rhoode which he converted himself.
SWD right wing Clinton Wagman narrowed the gap even more when he scored seven minutes later. Rhoode converted to make it 21-14 with 20 minutes to play.
SWD had a chance to pull the score level minutes later but a crucial knock-on just short of the tryline saw their chance go missing.
WP replacement Demetri Catrakilis kicked a penalty in the 73rd minute to give his team some breathing space before flank Rohan Kitshoff made sure of the win with a bonus-point try from driving play with two minutes left on the stadium clock.
It took Western Province 14 minutes to score their first points of the match when flank Tyrone Holmes crashed over for the opening try. Coleman had no problem with the conversion.
Three minutes later Coleman increased his side's lead when he sped over for the second five-pointer of the match. He converted his own try to take the score to 14-0 at halftime.
SCORERS:
SWD – Tries: Delroy Rhoode, Clinton Wagman; Conversions: Delroy Rhoode (2).
WP – Tries: Tyrone Holmes, Kurt Coleman, Nic Groom, Rohan Kitshoff; Conversions: Kurt Coleman (3); Penalties: Demetri Catrakilis.