Sweden's Fredrik Jacobson is alone in second place at 7-under-par 64. David Frost, the 1992 winner, is in third at minus-5.
This is the final tune-up for next week's U.S. Open and Singh, one of the favorites for this season's second major, cemented his status.
'When you have wedges and sand-wedges in, you're going to make a lot of birdies,' said Singh. 'I hit really close. I drove the ball beautifully. I attacked the course.'
Singh started on the back nine Thursday and struggled with a par and bogey at his first two holes. He rebounded with three birdies on his first nine, including back-to-back at 12 and 13, to make the turn at 2-under 33.
After the turn, the No. 3 player in the world caught fire. He ran home a 15-foot birdie putt at the second, then made it four in a row with three birdies from inside 5 feet.
Singh was not done tearing up the course. At the short of the seventh, Singh came up short of the green, but hit a beautiful chip that ran into chip-in range. He kicked in the birdie putt to match Jacobson in first.
Singh took over sole possession of the lead at the par-5 ninth. He landed in the fairway, then hit a fairway-metal into a greenside bunker. Singh blasted out to 2 feet and tapped in the birdie to come within one of Dan Sikes' 1967 course record.
'Last week I played well, I just didn't make any putts,' said Singh, referring to his share of 24th at the Memorial. 'I guess if you hit it close, you don't have to make too many of them.'
Jacobson had it going early with strong wedge play. He hit his approach to 5 feet to set up birdie at the second, then added another birdie putt from a foot longer at No. 3.
The Swede's round really took shape at the par-5 fifth. Jacobson hit a 3-wood to 60 feet and sank the putt that climbed two tiers before falling in the hole.
'It was a roller coaster,' said Jacobson, referring to the long eagle putt. 'It was straight on line and it's very rare you get the pace and everything right on a putt like that.'
Jacobson followed the eagle with a 10-footer for birdie at the sixth. He was on the fringe 13 feet away for birdie at the eighth, but the ball lipped out and Jacobson missed the par putt coming back. He reclaimed the lost stroke one hole later with a tap-in birdie and made the turn at 5-under 31.
Jacobson laid up off the tee at the 314-yard, par-4 10th and the decision paid off. He hit a wedge to 9 feet and holed the putt to go to 6 under for the championship.
His final birdie came at the 17th. Jacobson knocked a 58-degree wedge to 7 feet and rolled home the birdie putt to match his lowest score on the PGA Tour this season.
'It's always nice to post a good number early in a tournament,' said Jacobson, who also posted a 64 in the third round of the FedEx St. Jude Classic. 'When you start playing as good as I did the first six holes, you get into a tournament a bit quicker than you normally do.'
The last time Jacobson was this close to the first-round lead on the PGA Tour was at last month's Wachovia Championship, where he shared first. He withdrew before the second round then due to the birth of his first child.
'It feels extra nice to be back in the same position that soon after,' said the 23rd-ranked player in the world.
Fred Couples, Luke Donald, Jonathan Byrd, Loren Roberts, Peter Lonard, Kris Cox, Dudley Hart, Robert Damron and Roger Tambellini are tied for fourth place at 4-under-par 67.
David Toms, Davis Love III, Padraig Harrington and Memorial winner Ernie Els are among a group a stroke back at minus-3. Reigning Masters champion Phil Mickelson is in a logjam at 2-under-par 69.
Defending champion Jonathan Kaye opened with a 2-over 73 and is tied for 106th place.