SEOUL, May 11, 2014 (AFP) - The 27-year-old had shared the third-round lead with Park Sang-Hyun, but eased away on the back nine to finish the tournament at South Korea's Namseoul Country Club on 15 under par.
Lee Ki-Sang (67) and Hwang Jung-Gon (71) shared third place at nine under par, while Australian Scott Hend (72) was the best of the non-Koreans with a share of fifth at seven under.
Park only joined OneAsia the day before the tournament started, making the field through his membership of the Korean Golf Tour.
His previous best finish was joint second at their PGA Championship two years ago.
But he played like a veteran all week, shooting a tournament-low 64 in the second round and matching the day's best despite the pressure on Sunday.
"My putting was really great all week and that was the key," he said in comments supplied by the organisers. "I was really focused."
Leading final scores:
273 - Park Jun-Won (KOR) 72-64-70-67
276 - Park Sang-Hyun (KOR) 72-66-68-70
279 - Lee Ki-Sang (KOR) 70-73-69-67, Hwang Jung-Gon (KOR) 69-73-66-71
281 - Kim Woo-Hyun (KOR) 69-68-74-70, Park Il-Hwan (KOR) 70-69-71-71, Scott Hend (AUS) 71-66-72-72, Jang Dong-kyu (KOR) 69-72-69-71, Kim Nam-hun (KOR) 75-66-69-71
282 - Song Young-Han (KOR) 69-71-74-68, Ryan Fox (NZL) 73-71-70-68, Lee Dong-Min (KOR) 72-70-69-