Anthony Kim got his AT&T National title defence off to the best possible start at Congressional Country Club but will have tournament host Tiger Woods right on his tail going into Friday's second round.
American Kim shot a course-record, eight-under-par, bogey-free 62 on Thursday to set an early target for the late-starting world number one and then saw Woods post a 64 to take a share of second place overnight.
Woods was making up for lost time having missed last year's second edition of his own event, which benefits the Tiger Woods Foundation and honours US servicemen and women, due to injury.
Playing alongside Charley Hoffman and Lucas Glover, the man who succeeded him as US Open champion at Bethpage Black 10 days ago, Woods sent down seven birdies and one bogey on the par-70, 7,255-yard Blue Course for a 64 to match fellow Americans DA Points and Bryce Molder.
Veteran Australian Steve Elkington put himself in contention with a 65, while England's Justin Rose put bad recent form behind him, having missed three cuts in succession, with a three-under 67 that leaves him five shots behind Kim in a tie for ninth.
A Ryder Cup hero for the US at Valhalla last September, Kim has struggled with injuries all year and he admitted earlier this week his confidence had been at rock bottom after missing the cut at The Players Championship in early May.
Yet he has turned a corner recently with a tie for 16th at the US Open two weeks ago and last week's tie for 11th at the Travelers Championship.
That improvement continued at Congressional as Kim, starting early and playing the back nine first, made the turn at two under with a 33 and came home with six birdies in 28. He even missed a birdie putt at the last, the par-five ninth, but had the luxury of a tap-in for par and a 62.