Jimmy Walker, gearing up for his PGA Championship title defense, fired a five-under par 65 on Friday to take a two-shot lead at the halfway stage of the World Golf Championships Bridgestone in Akron, Ohio.
Walker shook off lengthy weather delays as thunderstorms disrupted action at Firestone Country Club.
He carded six birdies with just one bogey en route to a 36-hole total of seven-under 133.
Walker edged ahead of overnight leader Thomas Pieters of Belgium when he rolled in an eight footer for birdie at the 15th.
Pieters then fell further back with a bogey at the par-three 15th, where he was unable to get up and down from a bunker.
He had two birdies and two bogeys in an even par 70 for 135.
"I played decent," Pieters said. "I hit plenty of greens -- I think a bit less than yesterday. The driver was still a little bit off. Ball striking's been good, same today. Missed a couple short ones on 17 and 18, but rolling the putter nicely, so looking forward to this weekend."
It was a further stroke back to Rory McIlroy, Zach Johnson and Hideki Matsuyama on 136.
McIlroy, playing his first tournament since sacking longtime caddie J.P. Fitzgerald as he tries to turn around a so-far disappointing season, chipped in for birdie at the 16th en route to a one-under 69 while Japan's Matsuyama and America's Johnson both shot 67.
"Once we got back out there after the delay, I think everybody felt a little flat," McIlroy said of playing after the afternoon delay of more than three hours.
"I didn't help myself by missing a few chances as soon as we came back out. Luckily I found one birdie coming in."
Australian Jason Day turned in a four-under 66 to join a group of six players on 137 that also included British Open champion Jordan Spieth, who signed for a 70.
Day had charged up the leaderboard with four birdies in his first five holes and five birdies on the front nine.
But he appeared to tweak his troublesome back, and had two bogeys and a birdie coming in.
- Marathon day -
Organizers had moved up tee times in a bid to beat the weather and Walker, who was diagnosed with debilitating Lyme Disease in April, admitted the day "did feel like a marathon".
But he added that for him it was "a great day".
"(I) played solid, hit it well, made some putts -- just solid, a solid day of golf."
Walker, who hasn't lifted a trophy since making his major breakthrough at last year's PGA Championship, hasn't contended on the big stage this year. He missed the cut at the US Open and finished tied for 54th at the British Open, and said he wasn't thinking about his title defense at Quail Hollow next week.
"It's just important for me to have a good week," he said. "I haven't had too many this year, it's been kind of rough. But things have been trending, I feel like, and hopefully this is shades of things to come."