Otto finished the tournament at 14-under 274 for his second European Tour victory. He won the Italian Open in May 2008.
Bernd Wiesberger fired a 4-under 68 Sunday and finished second at 13-under. Thomas Aiken (72 Sunday), Richard McEvoy (68) and Ockie Strydom (69) finished tied for third at 11-under.
Otto opened the final round with a three-stroke lead but Wiesberger moved into contention with three early birdies. Wiesberger was 4-under after 11 holes but had a bogey at the 13th hole. A birdie at 15 left him at 13-under for the tournament.
Otto was 2-under through 12 holes Sunday but came back to the pack with three bogeys in a four-hole span before a 17th-hole birdie put him back in the lead.
He is the eighth South African to win the tournament. South African players have won the event 12 of the 16 time -- including 10 of the last 11 -- it's been contested.