American Pat Perez holed five birdies in the final six holes for a six-under 65 and a two-shot lead after the second round of the Wells Fargo Championship.
Perez was four shots off the pace at the 13th but a sensational 30-footer on the 17th helped him move to 12 under.
Jonathan Byrd and Bill Haas are two behind Perez on ten under while three-time Masters champion Phil Mickelson shot a superb 66 to move to nine under.
Defending champion Rory McIlroy carded a level-par round but missed the cut.
The Northern Irishman paid the price for a three-over first round of 75 while Englishman Paul Casey was another casualty, despite a much improved second round of 68.
Casey shot five birdies but his tournament was already as good as over after a woeful opening round which saw him resume on six over.
Mickelson was the day's main mover, his six-under second round leaving him well placed to challenge for the title at the weekend.
But Perez is the man to catch, although he admitted his stunning finish at Quail Hollow came as a surprise.
"That's not what I had in mind when I stepped on the 13th tee, let me tell you that much," he said.
"It was great to be on the course, and I knew I was playing well. It's nice to have peace on the course, and having some laughs and all that kind of stuff. It was nice. It was fun."