SEOUL, May 10, 2013 (AFP) - Kim had six birdies and a bogey around the hilly 6,349 metre (6,943 yard) course at the Namseoul Country Club to stand at 10 under for the one billion won ($900,000) tournament.
Kim Gi-Whan also shot 67 to finish in second place, while Kim Dae-Sub was a stroke further behind after posting 66 in drizzly conditions.
The course lived up to its reputation as a graveyard for foreigners, with Australian overnight leader Terry Pilkadaris (75) the best of the non-Koreans in joint 10th place and five shots off the lead.
Cho Min-Gyu (73), who shared the first round lead, was seven under.
"You can see it wasn't very good weather, so I am very happy with my score," said leader Kim Hyung-Sung, who has been plagued by a shoulder injury for the last two years.
"This tournament is always won by great players, so to do well here would be something special for me."
Defending champion Kim Bi-O came unstuck at the par-five 16th when his tee shot struck a tree, leaving him one under for the round and tournament so far.
"At least I'm in the red and anything can happen at Namseoul," he said.
Scores after round two: (par 72)
134 - Kim Hyung-Sung (KOR) 67-67
135 - Kim Gi-Whan (KOR) 68-67
136 - Kim Dae-Sub (KOR) 70-66
137 - Ryu Hyun-Woo (KOR) 72-65, Kim Do-Hoon (KOR) 67-70, Cho Min-Gyu (KOR) 64-73
138 - Choi Ho-Sung (KOR) 70-68, Mo Joong-Kyung (KOR) 70-68, Park Ju-Hyuk (KOR) 68-70, Lee Kyoung-Hoon (KOR) 67-71, Song Young-Han (KOR) 68-70