Rory McIlroy couldn't keep the bogeys off his card, but the four-time major winner offset that with five birdies to grab a share of the halfway stage lead at the BMW Championship on Friday.
Northern Ireland's McIlroy toughed out a one-under 69 to tie Patrick Cantlay at the top of the leaderboard for a one-stroke cushion heading into the final round of the second leg of the PGA Tour's FedEx Cup playoffs.
McIlroy and Cantlay are at one-under 139, making them the only players under par on the difficult Olympic Fields Country Club course in Illinois.
McIlroy, who won this tournament eight years ago, has carded just one top 30 finish since the Tour restarted, but he can never be counted out in playoff event. McIlroy has two career FedEx Cup titles.
"Pars are good out there," McIlroy said. "I was able to break par which is awesome. I got myself into a good spot going into the weekend."
Dustin Johnson birdied his final two holes for a 69 to vault into a tie for third with Japan's Hideki Matsuyama, who shot a three-over 73 to reach even-par 140.
Australia's Adam Scott, Brendon Todd, Louis Oosthuizen of South Africa, Tony Finau and Billy Horschel are tied for fifth at one-over 141, two strokes back of the leaders.
The Olympia Fields event features a 69-player field with no cut, and the top 30 in the rankings after this event advance to the Tour Championship.
The suburban Chicago layout, which hosted the 2003 US Open, has proved to be one of the toughest challenges on the Tour this year.
McIlroy, who is trying to win this event for the first time since 2012, had three birdies on his front nine and two on the back.
He started quickly with two birdies on his first four holes, including a five-foot birdie putt on the par three 13th hole followed by an eight-foot putt on the par-four 11th.
McIlroy birdied his seventh hole of the round (No. 16) and his first hole on the back nine to get to three under. But three bogeys over his final seven holes knocked some of the wind out of his sails.
After some sub-par results of late, McIlroy said he has been making adjustments with his clubs, especially his driver.
"I was just trying to find something that I could get it in play," he said. "I went to higher loft driver and a different shaft.
"If I can get it in play off the tee, then I can play from there. I wasn't doing that over the last few weeks."
Cantlay had four birdies and an eagle on the par-four 11th hole for a two under 68. He made double bogey on No. 16 but then closed with a birdie to move into a tie with McIlroy.
"I drove it pretty good actually, and I thought my way around the golf course really well," said Cantlay. "I got a couple of good breaks, and sometimes that's what it takes to get up at the top of the leaderboard."
Johnson finished up his round with an eight-foot birdie putt on 17 and then a 32 footer on the par-four 18 to get within one stroke of McIlroy and Cantlay.
"I am in a very good position, what with two guys under par it shows you that the golf course is very tough," said Johnson.
American Tiger Woods birdied No. 17 then closed with a 37-foot birdie putt on 18 to salvage something from a disappointing five over 75 to move into a tie for 55th.
The birdie on 17 snapped a string of three straight bogeys for the 15-time major winner and reigning Masters champion.
Defending champion Justin Thomas shot a four-over 74 and is tied for 45th, eight shots back of the leaders.