The Korean-American, one of the sports rising stars, carried on where he left off for the U.S. in Kentucky.
The 23-year-old held a two-shot lead over local Kim Jong-myung (66) in the $1 million Asian Tour event at the Woo Jeung Hills Country Club south of Seoul.
I have been touched by the support given to me by fans in Korea, Kim told Korean media. I want to repay them and need to stay focused for the rest of the tournament. I am American but I am also Korean. As a Korean, I am proud to be in the lead but there is still a long way to go.
The Californian-born Kim birdied the first three holes on a day in which only 33 of the 132-man field broke par.
I used my driver on almost every hole, Kim said. There is hardly any rough here so I am comfortable and I like it. I birdied the final hole which was nice.
Five players were tied for third at 5-under-67.
Ian Poulter, runner-up in the 2008 British Open and Europes best player at the recent Ryder Cup, shot a 2-under 69 for a share of 15th place.
I got off to a slow start but picked up the pace at the end of the front nine, Poulter said. I missed a few birdie chances. I played quite steady today and hopefully I can shoot better tomorrow.
New Zealander Mark Brown, who comfortably leads the Asian Tour order of merit, had a poor day, shooting a 7-over 78 to be fourth-last.