The 23-year-old South Korean calmly sunk his putt after Fisher missed a four-metre effort for par on the 18th, the first playoff hole, to win the $2 million (£1.23 million) event, co-sanctioned by the European Tour and PGA Tour of Australasia.
"I was nervous, I was shaking but I controlled myself pretty well all day I thought," Jin told reporters after carding a three-under 69 in the final round. "I don't know what I've done to be honest.
"I was struggling quite a bit when I was turning pro, but it was going to happen in the learning circuit I guess.
"I had played play-offs in mini tour events, but playing with Ross Fisher, he's one of my heroes. Playing with him in the play-off, it was unbelievable."
Trailing overnight leader Brody Ninyette by a stroke, Jin got off to a nightmarish start with a double bogey on the par-four first hole after four putting.
He kept his composure, though, to gain five strokes over his next 17 holes to finish tied with former Ryder Cup player Fisher on 10-under for the tournament after the Englishman finished shot a 68.
Jin, who has played on the Challenge Tour this season and was due to take part in the second stage of the European Tour's qualifying school, earned a two-year exemption after his victory.
Local hope Ninyette, who had a three-shot lead at one point, dropped three bogeys in his final six holes to finish two strokes off the pace.
He signed off with an even-par 72 to be tied for third spot with compatriot Dimitrios Papadatos and England's Danny Willett.
Fisher's runner-up finish with a closing 68 saw him climb to the top-60 in The Race to Dubai and should earn him a place at the World Tour championship next month.
"Obviously it would have been lovely to have come here and won, but that's golf," Fisher said.
"Unfortunately I came up a little bit short, but I can be very pleased the way I played today. I hung in there really well; it was always going to be tough.
"There are some good names up there and I knew I needed to just play really well. I felt like I did that."