An Byeong-hun and Im Sung-jae fired eight-under 62s to lead the Wyndham Championship as Jordan Spieth also made a fine start on Thursday.
An and Im shot bogey-free opening rounds at the Sedgefield Country Club to share a one-stroke lead in Greensboro, North Carolina.
The South Korean pair are both looking for their first wins on the PGA Tour, but top what is a congested leaderboard.
Spieth is part of a tie for seventh at six under after shooting a mixed 64 that included an eagle, six birdies and two bogeys.
— PGA TOUR (@PGATOUR) August 1, 2019
The 2013 runner-up, looking for his first win since 2017, is joined by Josh Teater, Webb Simpson, defending champion Brandt Snedeker, Brice Garnett, Seamus Power, Ryan Armour, Ted Potter Jr and Kiradech Aphibarnrat at six under.
Mackenzie Hughes, Rory Sabbatini, Patrick Rodgers and Johnson Wagner are ahead of that group after carding 63s.
Paul Casey made a decent start with a five-under 65, while Hideki Matsuyama opened with a 67.