Jimmy Walker shot a five-under 65 Friday at the World Golf Championship-Bridgestone Invitational to take the second-round lead.
Rain caused a couple of long delays, which forced players to persevere through a near 12-hour day to complete their rounds.
Walker, who dealt with symptoms from Lyme Disease earlier this year, made it around difficult Firestone Country Club (South) with six birdies and a bogey. He is seven-under for the tournament heading into the weekend.
Walker has not won since capturing his first major at last year's PGA Championship, but he looks poised to get his season back in gear this week.
Belgian Thomas Pieters grabbed solo second after firing an even-par 70 to remain at five-under. Pieters led after Thursday's first round, but he missed a number of short par and birdie putts on the back nine on Friday. Clearly hitting the ball with confidence, Pieters now needs to see some more putts drop.
Rory McIlroy, with new caddie Harry Diamond carrying his bag, shot a one-under 69 to get to 4 under for the tournament. With just two birdies and a bogey on his scorecard, McIlroy may be a little disappointed he didn't take advantage of his ferocious drives.
McIlroy did give the crowd a jolt on the 16th hole when he chipped in from behind the green for birdie.
Zach Johnson and Hideki Matsuyama are tied with McIlroy for third at four-under.
Jordan Spieth, who is in search of his third straight win, birdied his last two holes to get back to three-under for the tournament. Spieth nearly three-putted 16 to fall back to even par, but he drained a six-footer for par before sticking his approach shots in tight on the last two holes.
Jason Day, after playing alongside Spieth and McIlroy during the first two rounds, is tied with Spieth at three-under. Despite battling through noticeable back pain, Day shot a four-under 66.