Andrew Loupe earned the outright lead after the second round of the Wells Fargo Championship but the tournament's star names are charging in Charlotte.
Seeking his maiden PGA Tour title, Loupe carded a one-under-par 71 to maintain his one-stroke advantage at eight under on Friday.
Loupe - a winner on the Web.com Tour - shared a one-shot lead alongside countryman Steve Wheatcroft overnight but the former moved clear atop the leaderboard thanks to a final-hole birdie, having bogeyed his previous hole at Quail Hollow Club.
Roberto Castro is within touching distance of Loupe at seven under following his second-round 66, which included an eagle, seven birdies and three bogeys.
Chesson Hadley (67) and Mark Hubbard (68) are a stroke further back as the big boys close in on Loupe.
Five-time major champion Phil Mickelson is just three shots off the pace and tied for fifth.
Mickelson posted a two-under 70 to sit alongside Rickie Fowler, who had five birdies during his 68.
Wheatcroft (74), Brian Harman (70), Daniel Berger (71) and Scott Langley (69) are also five under through 36 holes, with Justin Rose (70) and John Senden (72) a shot behind.
Defending champion Rory McIlroy, meanwhile, showed glimpses of his best before a late collapse as he recorded a three-under-par 69.
McIlroy, who started the day one over and looked to be headed for another lacklustre round, had an eagle and three birdies on the front nine.
But after birdieing the 10th and 14th, McIlroy ended his round with back-to-back bogeys, leaving him six strokes off top spot heading into the weekend.