Chris DiMarco, who went 2-1-1 at the Ryder Cup last week, fired a 65 to move into third place at 9-under-par 135. Joey Sindelar, Kent Jones and J.P. Hayes were two shots further back at 7-under-par 137.
Singh has won seven times this season, but none of those were wire-to-wire wins. He is halfway to making win No. 8 wire-to-wire, and the top player in the game calmly made his way around the Mystic Rock Course at Nemacolin to carry the lead into the weekend.
'I played quite well today,' said Singh. 'The only difference was not hitting it as close as I did yesterday and not making the putts, but I did hit it close.'
He played the back side first and jumped out of the gate with a birdie at the par-4 10th after his second shot dropped within 8 feet of the hole. Singh then pitched his third to 4 feet for a birdie at the par-5 11th, but stumbled to a bogey at the very next hole.
Singh recovered at the 15th and drained an 18-foot putt for a birdie. He then hit his approach to 7 feet at the par-5 16th, but was only able to two-putt for a birdie.
At the par-5 fifth, Singh chipped his third shot from off the green within 3 feet of the hole for another birdie. Singh had a birdie chance at the par-5 eighth, but three-putted for par. He then parred the ninth to finish two shots clear of Curtis.
'Today I had another chance to shoot a low one,' said Singh. 'I gave myself a lot of chances for birdies.'
Curtis had an early start to his round and ran off five birdies over his first eight holes to jump to 10 under. The 2003 British Open champion faltered to a bogey at the 14th, but dropped his approach inside 9 feet at the last to take second place alone.
DiMarco also started on the 10th and collected three birdies on the back nine to make the turn at 5 under. The 36-year-old added four birdies on the front side to move into contention heading into the weekend.
'It's about time I made some birdies,' said DiMarco, who won this event in 2000. 'It was nice. I hit it close and I made a couple of good putts. I actually missed a couple too, I missed two 4-footers out there for birdie.'
Zach Johnson, Len Mattiace, Richard S. Johnson and Brent Geiberger are knotted at 6-under-par 138. K.J. Choi, Robert Gamez, Duffy Waldorf and Matt Gogel were one shot further back at 5-under-par 139.
A total of 74 players survived the 36 hole cut, which fell at 1-under-par 143. David Duval, who had made the cut in each of his last two events, will miss the weekend after a round of 74.
Former PGA champions Shaun Micheel and Rich Beem also failed to make the cut as well as Brad Faxon, Scott Verplank, Rory Sabbatini and last year's 84 Lumber Classic winner J.L. Lewis.