Padraig Harrington and Shane Lowry made steady starts to the Memorial Tournament as Jason Dufner and David Lingmerth shared the first-round lead at Muirfield Village.
Harrington made two birdies and a single bogey in a rock-solid round of 71 to lie six shots off the lead in a tie for 26th at one under par, while Lowry sits just one shot behind after a level par 72.
Dufner had to settle for a share of top spot after blotting his copybook at the end of the day. The former US PGA champion fired six birdies and an eagle to leave himself one shot clear of Sweden's Lingmerth heading to the 18th hole.
But his first bogey of the day on the par-four last saw him post a seven-under 65.
"I hit a lot of fairways, lot of greens, which gave me a lot of opportunities," Dufner said. "I'll take it. Sixty-five to start the tournament is a good place to be."
Jordan Spieth and Daniel Summerhays are a shot further back on six under but defending champion William McGirt is off the pace after carding a 71.
World number one Dustin Johnson faces a battle to make the cut after failing to make a birdie in his six-over 78.
After Lingmerth had set the pace in Ohio with eight birdies and an eagle in his 65, Dufner launched his bid for a fifth PGA Tour title by covering the front nine in 31.
Further birdies on the 11th, 14th and 15th left Dufner on eight under but he was unable to complete a flawless round.
Spieth, one of six top-10 players in action at Muirfield Village, enjoyed another encouraging day after returning to form in his home state of Texas last week.
It would have been an even better round for the world number six had he not bogeyed the final two holes.