World No.1 Jason Day birdied two of his last three holes, despite difficult conditions, to take a one-stroke lead after the wind-swept second round of the latest World Golf Championship event in Ohio
The game's hottest player over the past 12 months with seven tournament wins, Australian Day had a three-putt bogey at the last to card 69 for a four-under total of 136 at Firestone Country Club.
The 28-year-old laid up in two at the par-five 16th before hitting an exquisite wedge to five feet and sinking the birdie putt, and then picked up another shot at the 17th, where he drained a 16-footer from the fringe to earn the outright lead.
After an opening round eight-over-par 78, New Zealand's Danny Lee carded a 71 on day two to tie for 51st, 13 strokes behind Day.
Swede David Lingmerth was alone in second after firing a best-of-the-day 67. One stroke further back were first-round leader William McGirt (74), fellow American Scott Piercy (69) and Argentina's Emiliano Grillo (71).
"One of those days where you had to really stay patient ... it was really difficult to make birdies," said Day, who is bidding for a fourth PGA Tour victory this season.
"The greens are starting to get firm and fast, the fairways are firm and fast and then you have a 15 mph (24 kph) wind. I'm just very pleased to shoot under par."
Seventeen players were under par after the opening round but only nine were left in red numbers after 36 holes, having battled in shifting winds on a daunting Firestone layout running firm and fast with a premium on driving accuracy.
Lingmerth, who clinched his first PGA Tour victory at last year's Memorial Tournament and lost a playoff for the CareerBuilder Challenge in January, made a storming start with four birdies in his first nine holes, before dropping one shot on the inward half.
"Today was a scrambling sort of day for me," Lingmerth told Golf Channel. "I putted really well, chipped well round the greens, but wasn't able to strike the ball as well as I have been the last few months. It was a big grind today."
World number two Jordan Spieth, who salvaged a poor day from tee to green in the opening round with brilliant putting, remained in contention as he carded a 71 to sit just three strokes off the pace, level with fellow Americans Justin Thomas (69) and Kevin Kisner (70), and Australian Adam Scott (68).