Clark, of South Africa, shot a 66 in the final round for a total of 15-under-par 273. He also won the event in 2002.
"It means a great deal to win our national open and again to win here at Durban Country Club," Clark said.
The tournament is part of the European Tour's international schedule.
Millions of Getty images now available for free via embed tool
Ray Liotta sues skin care company over use of likeness