Seamus Power is in a six-way tie for second after a fine second-round six-under-par 66 left him 11-under at the Rocket Mortgage Classic.
The Waterford man sits alongside Americans Matthew Wolff, Bryson DeChambeau, Ryan Armour, Richy Werenski and Mark Hubbard.
Power shot six birdies on Friday to remain right in the mix heading into the weekend.
Chris Kirk, who carded a scorching 65, and Webb Simpson lead the way on 12-under.
Simpson, seeking wins in consecutive starts after a triumph in South Carolina 12 days ago, birdied seven of his first 13 holes and moved into a share of the lead when he holed out from a greenside bunker at the par-four 16th.
"I came in confident, I came in feeling good about my game," the former US Open champion said.
"Most guys I feel like play well out here when they're not really thinking a whole lot, their mind is calm and they feel in control and they feel confident. That's kind of where I am right now."
World number 10 DeChambeau (67), who started on the back nine, came agonisingly close to capping his bogey-free round with an ace at the par-three ninth where his tee shot settled two-feet from the cup.
"Coming off with a clean card today makes me feel really good, and finishing off with a birdie gives me some inspiration for tomorrow to play well," said DeChambeau, who has top-eight finishes in all three PGA Tour events since play resumed.
Rickie Fowler (71) offset two front-nine bogeys with back-to-back birdies starting at the 12th hole to get inside the cutline and added another at the penultimate hole to sit six shots back of the leaders.
Defending champion Nate Lashley (69) closed his round with a bogey and missed the cut by one stroke.
Among those who missed the cut are former major champions Vijay Singh, Jason Day, Bubba Watson, Patrick Reed, Jason Dufner and Charl Schwartzel.