Jimmy Walker fired a 65 to lead the way on a weather-affected second day of the WGC-Bridgestone Invitational but had Thomas Pieters and Rory McIlroy breathing down his neck at Firestone Country Club.
After a 45-minute delay at the start of the day due to the threat of lightning, two further suspensions saw four hours and five minutes lost, with a spell of torrential rain in the early afternoon.
When the hooter sounded for the second time to spark a three hour and 19 minute delay, Walker and Pieters shared the lead at five under but the American picked up two birdies on the back nine to open up a two-shot advantage.
McIlroy was then in the group at four under after a 69, alongside World Number Three Hideki Matsuyama and 2015 Open champion Zach Johnson.
Russell Knox was a further shot back alongside Alex Noren, with Tommy Fleetwood then at two under.
Walker - who will defend his US PGA Championship title next week - has struggled this season after suffering with Lyme disease but showed all the qualities that made him a Major champion on Friday as he brushed off all the distractions to fire the lowest round of the day.
"It's nice to see some putts go in and make some solid swings and keep rounds going, make some par putts, just the stuff I haven't been doing."
The 38 year old made a fast start with birdies on the second, third and fifth and while he dropped a shot on the seventh, he regained it on the next. His back nine was then a tale of the par threes as he put his tee-shot to the 12th to two feet to take the lead and his first to the 15th to eight feet.
The latter birdie moved him back ahead after Pieters had caught him at the top of the leaderboard with the help of a remarkable shot on the tenth.
The Ryder Cup star entered the day with a one-shot lead and while he started with two poor shots to bogey the first, he took advantage of the par five next to sit level par for the day at the turn.
He found sand off the tee on the first hole after the turn but hit a stunning bunker shot round the trees and to five feet to keep the pressure on Walker.
Pieters was not so impressive from the sand at the 15th, however, and after he failed to get up and down, Walker led by two.
"I played decent," said Pieters. "Again, I think 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, the same today. I missed a couple of short ones on 17 and 18 but I'm rolling the putter nicely so I'm looking forward to this weekend."
McIlroy was another player to capitalise on the gettable second but he failed to get on in regulation and dropped a shot on the ninth. He followed that with six pars and after finding rough with his first three shots on the par five 16th, the four-time Major winner chipped in for a birdie.
Scotsman Knox had been seven under after starting with three birdies but a hat-trick of bogeys from the 11th saw him fall down the leaderboard.
Swede Noren was over par at the turn but birdies on the 11th, 13th, 16th and 17th sent him in the other direction.
Australian Jason Day turned in 30 but looked to be struggling with his back in a 66 that got him to three under alongside Champion Golfer of the Year Jordan Spieth, fellow American Charley Hoffman and Canada's Adam Hadwin.
Fleetwood signed for a two under par 68.
Hudson Swafford made the 25th hole-in-one of the season and first here since 2011 as he aced the 15th from 214 yards.
