Van Der Walt -- one of three golfers sharing the lead at the start of the final round -- drained a birdie on the 12th to grab the lead for good, then iced the win with another birdie try at No. 15. He finished at 21-under 267.
Darren Fichardt carded a 3-under 69 to end alone in second at minus-19, while Louis De Jager also registered a 69 to grab third one shot further back at 18-under 270 at Copperleaf Golf & Country Estate.
Peter Uihlein of the United States turned in a round of 69 as well, good for fourth at minus-17.
Third-round co-leader Charl Coetzee ended up in a fifth-place tie after carding an even-par 72.