Englishman Daniel Brooks had held a three-shot lead after the second round in Durban, which was only completed earlier Saturday because of the weather delays, but struggled with five bogeys and a double bogey in his final-round 76.
Van der Walt, who was tied for second heading to the final 18 holes, made five birdies and an eagle to go with three bogeys on the Mount Edgecombe course. Coming in, he recovered from his third bogey at No. 11 by making eagle at No. 12 and birdie at No. 13. The South African also caught a break on the par-5 No. 14 when a shot heading toward the rough bounced favorably for him.
Neither Baldwin nor Campillo could apply enough pressure in the final stretch, with Baldwin making just one birdie in his last 11 and Campillo crucially dropping a shot at No. 15. Campillo and Colin Nel on Friday became the first players to card 59s in a European Tour event, although their scores don't count as records because players were given preferred lies on the rain-soaked course.
France's Romain Wattel was alone in fourth on 12 under and South Africa's Oliver Bekker fifth on 11 under. American John Hahn finished in a four-way tie for sixth alongside four-time European Tour winner Branden Grace.