Dustin Johnson shot a bogey-free 5-under 65 on Thursday to take a one-stroke lead after the first round at Colonial.
Hunter Mahan, playing in the group ahead of Johnson, had the lead before a double-bogey 6 at the 433-yard 18th. With a 66, Mahan was tied for second with Harris English, Tim Wilkinson and Robert Streb.
Adam Scott was tied for 64th at 71 after his first round as the No. 1 player in the world. Scott had four bogeys in his first nine holes.
Jimmy Walker, a three-time winner this season, was in the group at 67.
Johnson's 65 was the highest score to lead after the first round at Hogan's Alley since another 65 in 2002. There were two opening 62s the previous three years.