South Korea's Choi Jinho ended the final round with a stunning eight-under-par 64 but could not reel in Harding.
"It was nerve-wracking, especially coming off. It's a situation I haven't really been in," said Harding, who bogeyed the sixth and seventh holes.
"I didn't enjoy it but it's good fun, I'm glad it happened and now we move on. I'm looking forward to seeing what happens going forward and playing in some bigger events."
England's Oliver Wilson, who had a one-shot lead after the third round on Saturday, also finished tied for second place, two strokes behind.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Others who finished tied for second in the closely-fought event include Harding's compatriots George Coetzee, Erik Van Rooyen and Christiaan Bezuidenhout, Spaniards Nacho Elvira and Jorge Campillo, Swede Anton Karlsson and Frenchman Mike Lorenzo-Vera.
Harding is the fifth South African to win the event after Darren Fichardt, Ernie Els and Retief Goosen plus Branden Grace, who won back-to-back titles in 2015 and 2016.
(Reporting by Rohith Nair in Bengaluru; editing by Clare Fallon)
