Hideki Matsuyama shot a 3-under 67 on Thursday to secure the first-round lead at the BMW Championship.
Matsuyama overcame two early bogeys and a 1-over outward nine by closing cleanly with five pars and four birdies, highlighted by two gains in his three final holes.
Following a three-birdie, one-bogey round of 68, Tyler Duncan was alone in second-place on 2 under, one clear of Mackenzie Hughes (69), who was the only other player in the red after day one at Olympia Fields.
A group of 10 players were tied for fourth-place at even-par 70, headlined by Rory McIlroy, who offset four bogeys with four birdies.
World No. 1 Dustin Johnson was among a group of seven tied at 1-over 71, one ahead of 14 more deadlocked at 2-over, including Bubba Watson, Adam Scott, Kevin Kisner, and Louis Oosthuizen, among others.
Defending champion Justin Thomas bogeyed four of his last six holes, including his final three to tumble from the top of the board down to T35 on 3-over par. Tied with Thomas were some of the biggest names in the field, including Tiger Woods, Patrick Reed, Daniel Berger, Xander Schauffele, Bryson DeChambeau, and Tyrrell Hatton.
Pos-Player-To Par (Score)
1. Hideki Matsuyama -3 (67)
2. Tyler Duncan -2 (68)
3. Mackenzie Hughes -1 (69)
4. 10 Players tied E (70)