Perth-based Ninyette led the tournament by one shot from Jeong entering the final round and held his nerve for most of the day in only his second European tour event.
The indigenous Australian player was still in front after 12 holes but bogeys at the 13th, 16th and 18th holes dropped him back to 8-under and he finished with an even-par 72 and a tie for third with compatriot Dimitrios Papadatos and England's Danny Willett.
Fisher, playing in the group ahead of Jeong, had six birdies and two bogeys in his final round. His birdies at the 15th and 17th holes carried him to 10-under and he was briefly the clubhouse leader before Jeong parred the 18th to force the playoff.
The players returned to the 18th tee and, after a steady approach, Jeong sank the decisive putt from two feet while Fisher three-putted for bogey.
"The first hole was a wakeup call I guess and after that I settled in pretty well and played pretty well," Jeong said. "Putting was really the key. I rolled the ball really well and put in a lot of good putts."
American Dustin Johnson shot the best round of the day, a 66, to rise into a tie for 12th place while compatriot Bo Van Pelt finished in a tie for 18th at 3-under.