Nate Lashley produced a superb nine-under par 63 to take a six-stroke lead heading into the final round of the Rocket Mortgage Classic.
The American, who was added to the field as a late addition following David Berganio's withdrawal, had a bogey-free card around the Detroit Golf Club to stand at 23-under.
Compatriot JT Poston sits in second place following his six-under 66, which could have been lower but for a bogey at the par-four sixth.
Cameron Tringale climbed up into third place after his 65 put him at 16 under, having dropped a shot at the 18th.
One shot back is 2018 Masters champion Patrick Reed, who had two bogeys in his own seven-under round.
Cameron Champ, however, plummeted down the leaderboard after signing for a 75 - some 10 strokes worse than his second round when he had recorded a career-best nine-hole score of eight-under 28.
The American recovered from a bogey at the third, only to then make a five on the par-three fifth.
He dropped another shot on the ninth, added further bogeys at the 12th and 17th holes before finishing with a birdie.
Ryan Armour's challenge also fell back after a run of six bogeys on the back nine, having turned at three under, to finish with a 74.
England's Luke Donald made 72 and sits in a group of players on eight under, alongside American Rickie Fowler.