World number one Jason Day took over at the top of the leaderboard after two rounds of the WGC-Bridgestone Invitational in Ohio.
The Australian, seeking his fourth win of the season and his ninth victory in his last 20 starts, had an eventful finish at the Firestone Country Club, Akron.
Day started the second round three shots off the pace and had an eventful finish, with birdies at the 16th and the 17th followed by a bogey - leaving him on four-under-par.
However, the one-under round of 69 proved enough to give him a one-shot lead over Sweden's David Lingmerth, whose impressive short game meant he carded a 67.
Day found the windy conditions a challenge, telling Sky Sports afterwards: "My short game saved me. I'm very pleased to shoot a 69 from some of the positions I was in today.
"It was really difficult to try to pick clubs and stay committed to it - but over the weekend it'll probably die down a bit."
A double bogey at the last damaged the hopes of overnight leader William McGirt, whose 74 meant he joined Argentina's Emiliano Grillo and America's Scott Piercy a further shot back.
Four players were sharing sixth position on one under - Australia's Adam Scott (68) and American trio Justin Thomas (69), Kevin Kisner (70) and Jordan Spieth (71).
Ireland's Shane Lowry - who fired a 72 - is 12 shots off the pace.