After leading from start to finish, 50-year-old Choi ended the tournament at the Nam Seoul Country Club with a 10-under total of 278.
'This is my home course where I've been the club pro for 15 years,' said Choi, who enjoyed strong support from the hometown crowd all weekend. 'After taking the first round lead, I was very anxious and couldn't eat or sleep well this week. It is really nice to win.'
Thailand's Thaworn Wiratchant (70) finished second, three strokes back. The finish moves him to the top of the Asian Tour Order of Merit over fellow Thai Thongchai Jaidee.
South Korea's Sung Si-woo finished a stroke behind Thaworn for third, while South Korean amateurs Kim Kyung-tae and Kim Hyung-tae were joint fourth two strokes further back.
Thaworn narrowed Choi's lead to just one stroke after making three birdies on the front nine. But he bogeyed the 11th to give Choi breathing room and a chance for his experience to show.
Choi birdied the 13th and 17th, before Thaworn drained his birdie putt on the 18th to close the gap to three strokes.
'I was very nervous as Thaworn and Sung were catching up on me. After finding the fairway on the 18th hole, only then was I confident of winning the title.'
Thaworn said he'd been rattled by the cheering for his South Korean playing partners.
'But I played nicely and I'm happy to become the new Order of Merit leader,' Thaworn said.
Choi takes over as the oldest Asian Tour winner from Thai Boonchu Ruangkit, who was 47 years old when he won the Thai Open last season.
Australian Scott Barr added to the final round action with an albatross on the par-5 fourth hole, the first on the Asian Tour in nearly two years. Taiwan's Hong Chia-yuh shot the last albatross at the Maekyung Open two years ago.
Barr shot a final round of 70 to finish at joint 37th.
The Maekyung Open is the 14th leg of this season's Asian Tour.
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