Ireland's Padraig Harrington is tied for 31st place on three under par after shooting a respectable 68.

Choi started on the back nine at the Westchester County Club' s West Course, notching one of his four birdies at the 10th. He also eagled the par-four eighth before giving a shot back on his final hole.

"I'm very happy to have played the way I did this week, the past two days. I figured that two-under every day would be a good score for the tournament," Choi said.

"But now that I am at 12-under, I'm very excited being in the position that I am right now."

The 37-year-old has been playing his best golf of the year in recent months, winning the Memorial Tournament in June and the AT&T National in early July.

Seeking his seventh career win on the PGA Tour, Choi never has won more than two events in a single season. Since the beginning of 2000, eight players have won three or more events in a season, led by Tiger Woods, who has victorious seven times.

First-round leader Rory Sabbatini, who shot 63 on Thursday, tumbled four shots off the lead after an even-par 71 in the second round.

Geoff Ogilvy and Steve Stricker surged to within four shots of the lead. Winless since taking the 2006 US Open title, Ogilvy shot a five-under 66 while Stricker recorded a four-under 67 for the second consecutive day.

Ernie Els, Sergio Garcia and Adam Scott are among seven players tied at six under.

Phil Mickelson, who has finished no better than 32nd since winning the Players Championship in May, is seven strokes off the lead at five-under 137.

Three-time Barclays winner and defending champion Vijay Singh finished at four-over 146 through 36 holes and failed to make the cut, which was even-par.

One player missing among this week's 144 entries is Tiger Woods, who has cited fatigue following a busy summer schedule. The world number one won the USPGA Championship two weeks ago at steamy Southern Hills.