Jimmy Walker had six birdies in a 5-under 65 to take the lead of the PGA Championship after the morning flight of 78 golfers.
It tied Walker's career low round in a major.Emiliano Grillo and Ross Fisher were one shot behind while Harris English, James Hahn and Andy Sullivan were two strokes back.
Eight golfers posted 2-under 68s including defending champion Jason Day, Rickie Fowler and K.J. Choi.
The featured group of the morning wave had Day, Phil Mickelson (71), the winner the last time the PGA was held at Baltusrol Golf Club, and two-time PGA champion Rory McIlroy (74).