Koepka hits the front at St. Jude Classic

"I still feel like I could be five- or six-under-par more. I really haven’t been firing on all cylinders but it’s good enough to be at the top,” Koepka told reporters.

(Reuters)

Cook is playing on a sponsor’s exemption but is trying to prove that he belongs on Tour.

“I feel like I should be out here,” Cook said. My irons were on fire and I holed some putts.”

Australian Steven Alker is a shot further back, and a group of seven players are bunched at six under. Alker, who started on the 10th, had a hot stretch coming home on the front nine, reaching 10-under par before finishing bogey, double bogey to fall back.

Five-times major winner Phil Mickelson, who will head to Chambers Bay searching for a first U.S. Open win after posting a record six runner-up spots, managed a one-under-par 69 that leaves him at three under.

(Writing by Jahmal Corner in Los Angeles; Editing by Peter Rutherford)