World number one Jason Day has taken a one-shot lead at the WGC-Bridgestone Invitational at a tricky Firestone.
The Australian fired a one-under 69 in Akron, Ohio, on Friday to move to four under.
Day is a shot clear of Swede David Lingmerth and two ahead of overnight leader William McGirt, Emiliano Grillo and Scott Piercy.
One-time major winner Day mixed three birdies with two bogeys, including a blemish at the last.
He made birdies on 16 and 17, the latter from 16 feet, before narrowly missing his attempted par save on the last.
Nonetheless, Day will take a lead into the weekend after McGirt in particular struggled.
The American carded a four-over 74, battling on the back nine.
McGirt was even par through his first nine holes, but had a double bogey and two bogeys to finish.
His day was summed up on the last, where he found the bunker to produce a six and slip back into a tie for third.
Lingmerth was far more impressive with a 67, while Grillo (71) and Piercy (69) were solid.
Jordan Spieth and Adam Scott are among those lurking just behind.
World number two Spieth had a 71 to be at one under alongside Scott (68), Justin Thomas (69) and Kevin Kisner (70).
Rickie Fowler is also in contention despite a 73 leaving him at one over.
Defending champion Shane Lowry, however, continued to struggle and sits at eight over.