SEOUL, 14 May 2015 (AFP) - The 16-year-old high-school student, who won a silver medal with South Korea's national team at last year's Asian Games, hit seven birdies and two bogeys as he bids for the one billion won ($916,000) title.
"It is certainly a surprise but I have been playing well. Just need to keep my focus for the rest of the tournament," Kim said.
Australian veteran Jason Norris kept it tight around the hilly 6,353 metre (6,947 yard) course at the Namseoul Country Club to share second place on 68, with South Korea's Kim Gi-Whan.
Gareth Paddison from New Zealand and South Korean defending champion Park Jun-Won were joint fourth at three under par.
Harry Bateman of New Zealand, carrying his own bag after his caddy failed to appear before tee time, was three shots off the lead in joint sixth place.
Leading first-round scores (South Korean unless stated, 'A' denotes amateur):
67 - Kim Young-Woong (A)
68 - Jason Norris (AUS), Kim Gi-Whan
69 - Gareth Paddison (NZL), Park Jun-Won
70 - Harry Bateman (NZL), Steve Jeffress (AUS), Im Sung-Jae (A), Kim Woo-Chan
71- Ahn Myung-Hoon, Kim Yeong-Su, Kim Tae-Hoon, Moon Kyong-Jun, Hong Soon-Sang, Kim Do-Hoon, Lee Tae-Hee, An Jae-Hyun, Martin Kim (ARG)