Sterne shot a bogey-free 64 to finish with a tournament record total of 27 under at the Royal Johannesburg & Kensington golf course and win by the largest margin in tournament history.
"That was probably the best final round of my career," Sterne said. "It was quite special to finish the way I did."
Fellow overnight leader Trevor Fisher Jr. faltered on the final day, allowing Sterne to finish well clear of Charl Schwartzel (66) in second. Fisher eagled the first but sank to a 1-over 73 that dropped him to joint sixth, despite sitting five shots clear of the field with Sterne at the start of the final round.
Fisher eagled the first but sank to a 1-over 73 that dropped him to a tie for sixth, despite sitting five shots clear of the field with Sterne at the start of the final round.
The victory was Sterne's first since the 2008 South African Championship, and represented a major milestone for the 31-year-old player, who led at the halfway stage of last week's Omega Dubai Desert Classic before finishing second to Stephen Gallacher.
Sterne had risen to 29th in the world rankings following back-to-back successes on home soil in December 2008, but then dropped out of the top 1,000 after a form of arthritis in his back forced him to miss most of the 2010 and '11 seasons.
"After all the hard work and the time out with injury, I did think whether I was ever going to win again," Sterne said. "At one point the pain was so bad that I even wondered if I'd ever play golf again. But now I know I can."
Ricardo Santos of Portugal matched Sterne's final-day score of 64 to earn a share of third place alongside Chilean Felipe Aguilar (67) and South African George Coetzee (67).