Making his first appearance at TPC River Highlands, the 23-year-old Texan had eight birdies and a bogey in his afternoon round after tying for 35th last week in the U.S. Open at Erin Hills.
Johnson Wagner and Connecticut native Brett Stegmaier each shot 64 in the morning.
Stegmaier had seven birdies in a nine-hole stretch in the middle of the round and closed with a bogey on No. 9. He grew up in Madison, about 25 miles from the course.
Rory McIlroy, also playing for event for the first time, had a 67. Jason Day shot 72. They missed the cut in the U.S. Open.