Collin Morikawa edged into a one-stroke lead at the Workday Charity Open, while Jordan Spieth struggled during the opening round on Thursday.
Morikawa carded a seven-under 65 at Muirfield Village to hold a narrow advantage over Adam Hadwin.
A one-time PGA Tour winner, Morikawa made an eagle and six birdies before dropping a shot at the last hole.
After a top-10 finish at the Charles Schwab Challenge, former world number one Spieth has struggled in two events since and opened with an even-par 72.
The three-time major champion was three over through 13 holes before a birdie at 14 and an eagle at the par-five 15th saw him sit in a tie for 64th.
Hideki Matsuyama, Zach Johnson, Nick Taylor and Aaron Wise made brighter starts, shooting five-under 67s to be tied for third.
Justin Thomas, the world number five, is a shot further back in a group of 11 players who carded 68s.
Thomas recorded top-10 finishes at the Charles Schwab Challenge and RBC Heritage before missing the cut at the Travelers Championship, but the American is back in contention.
Pat Perez, Louis Oosthuizen, Tim Wilkinson, Peter Malnati, Patrick Reed, Ian Poulter, Adam Long, Graeme McDowell, Roger Sloan and Chase Seiffert are alongside Thomas at four under.
Brooks Koepka, meanwhile, battled to a two-over 74.