The visitors were gifted two early penalty tries by referee Stuart Berry, who also dished out a yellow card to Cell C Sharks XV lock, Lunga Ncube, midway through the first half, easing them into a 21-13 lead at the break at KP2, Kings Park.
The Cell C Sharks XV would have the better of their opponents at halftime had it not been for the poor discipline as they raced into an early 13-point lead thanks to a try by Kwanda Dimaza, which was converted by Rhyno Smith, who also slotted two penalties inside 11 minutes.
But that efforts fell apart midway through the first stanza as DHL WP were awarded their first penalty try, along with Ncube's sin-bin. With the visitors finally finding their stride and putting the home side under immense pressure, referee Berry was left with no choice but to award Province with their second penalty try after numerous warnings to the Durbanites.
Van der Merwe then scored the first of his two tries, rounding off an excellent move with the home side down to 14 men. Flyhalf Abner van Reenen converted, leaving the visitors in front at the break.
The Cape side began the second stanza in style and Van der Merwe raced away to score his second straight from the kick-off and with Van Reenen converting, Province moved their advantage out to a comfortable 15-point lead.
The Cell C Sharks XV struck back just moments later.
The home side worked their way up the park and into striking distance and flanker Vosloo forced his way over to reduce the deficit back to eight points with Smith converting.
But that would be the last time the hosts troubled the scorers. The visitors took complete control with Paul de Wet sniping over to take the former champions back out to 15-points to the good. The final 10 minutes saw the visitors score twice more through Marno Redelinghuys and Craig Barry to secure their third-consecutive victory and maintain their unbeaten stature in the tournament.
Cell C Sharks XV - Tries: Kwanda Dimaza, Wian Vosloo. Conversions: Rhyno Smith (2); Penalties: Smith (2).
DHL Western Province - Tries: Edwill van der Merwe (2), Paul de Wet, Marno Redelinghuys, Craig Barry, Penalty Tries (2). Conversions: Abner van Reenen (4).