Newtown Square (Pennsylvania): K.J. Choi of South Korea birdied five of his last six holes for a six-under-par 64 that tied the course record and gave him a two-shot lead after two rounds of the AT&T National on Friday.
Choi capped his sizzling round with a one-foot tap-in for birdie at the 605-yard, par-five ninth after his approach shot nearly fell into the cup. He stood at seven-under-par 133.
Americans Justin Leonard (67), Chris Riley (66) and Bo Van Pelt (66), and Charlie Wi (66) of South Korea shared second place at five-under-par 135.
Four players were tied on 136, including American Jeff Overton, who fired a 65 to get back into contention.
Choi, who missed the cut in his last start at the U.S. Open two weeks ago, caught fire on Aronimink`s front nine after beginning his morning round at the 10th.
His final birdie matched the 64 shot by 2010 champion Justin Rose of Britain in the second round last year.
Choi said he had not been aware what the course record was.
"But as I kept making birdies, I noticed that the reactions of the gallery, the people were very positive and I started feeling that I`m working toward a special round," he said through a translator.
"I`m not really a records kind of guy. I don`t really pay attention. My style is just playing hole by hole, trying my best each hole, each shot. When I heard I tied the record, I felt very happy, very pleased about that."
Choi won the inaugural AT&T National when it was played at Congressional in Bethesda, Maryland, in 2007. The tournament was switched to Aronimink a year ago so that Congressional could prepare the course for this year`s Open, and it will return to Congressional for the next three years.
Choi will try to become the first player to win the event hosted by Tiger Woods twice and add to his victory earlier this season at the Players Championship.
First round co-leader Adam Scott of Australia followed his opening 66 with a one-over-par 71 and was at three-under 137, a total he shared with American Rickie Fowler.
American Hunter Haas, who also had a 66 Thursday, posted a 74 in the second round and faded out of contention.