Spaniard Sergio Garcia and American Dustin Johnson each shot a four-under-par 67 in the first round on Friday (local time) in Illinois.
Garcia, whose round began at the 17th hole at Bolingbrook Golf Club, used a run of four birdies at Nos.11-14 to jump to six under for his day. However, he finished with back-to-back bogeys to give up the solo lead.
Lucas Herbert leads the Aussie charge, two shots behind the leaders after carding a two-under 69 in the first round.
Cam Smith and Marc Leishman are two shots further back after each opened with an even-par 71.
"Yeah, obviously you never want to finish bogey-bogey," Garcia said.
"I think at the end of the day four under is a very good score. I would have taken it at the beginning of the day with the conditions and the wind and everything, so I'm not disappointed about that."
Johnson also started his round at No.17 and overcame two early bogeys to also climb to four under.
The American has contended that his scores this season aren't reflecting the quality of his play.
"I feel like I'm always close, and it only takes a couple shots here or there where my game just clicks back and I start playing good again," Johnson said.
"Got off to a little bit of a shaky start today but then started hitting some quality shots and rolled in a couple putts and kind of turned it around and finished off with a nice solid day today."
They hold a one-stroke lead over six high-profile players: Americans Phil Mickelson, Brooks Koepka and Bryson DeChambeau, Spaniard Jon Rahm, England's Tyrrell Hatton and South Africa's Dean Burmester.
Mickelson's day resembled Garcia's. He had a strong start, with four straight birdies from Nos.12-15, but that was partially undone by bogeys at No.17 and No.18.
"I'm not really pleased with the finish. I need to be able to finish these rounds a little bit better. But I played well, hit a lot of good shots, and I really enjoy the golf course," Mickelson said.
Another seven players are two off the pace at two-under 69, including Australian Herbert.
In the teams competition, the South African outfit Stinger GC combined to go six-under on Friday, good for a one-shot lead over Garcia's Fireballs GC.
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