He won the FedEx St. Jude Classic in June in Tennessee for his first PGA Tour victory.
"I was a lot more comfortable out there than I was a Memphis," English said.
English and Rory McIlroy are the only current players under 25 with multiple PGA Tour victories.
Brian Stuard shot a 67 to finish second.
Third-round leader Robert Karlsson had a 72 to drop into a tie for sixth at 15 under.
"I've been struggling with the long shots, in general," the 44-year-old Swede said. "Usually, you get found out sooner or later. ... I'm still very, very pleased."
Jason Bohn (68), Chris Stroud (68) and Rory Sabbatini (70) tied for third at 16 under.
Justin Hicks (67), Justin Leonard (67) and Charles Howell III (69) joined Karlsson at 15 under.
More than 4 inches of rain hit the course from Wednesday to Friday. Because of the wet conditions, players were allowed to use preferred lies.