Washington - Jason Dufner powered to a seven-under par 65 on Thursday to join Sweden's David Lingmerth atop the Memorial leaderboard, with Jordan Spieth one adrift and top-ranked Dustin Johnson nowhere.
Sweden's Lingmerth, winner of the Jack Nicklaus-hosted PGA Tour event in Dublin, Ohio, in 2015, set the target early with a morning round that included eight birdies and one eagle, with three bogeys.
Dufner answered with a stellar afternoon that saw him hit the first 17 greens in regulation on the way to six birdies and an eagle before his only bogey of the day at 18 dropped him into a tie for first.
The leading pair were one stroke in front of Spieth and fellow American Daniel Summerhays on 66.
"I caught some breaks when I missed the fairway and still had some fairly good opportunities from the rough," Lingmerth said. "I consistently put myself in good spots around the greens and was able to roll a few in."
His lackluster results so far this season, however, had Lingmerth sounding a note of caution.
"It's a very humbling game," he said. "There's a lot of work ahead this week and weeks to come obviously so I'm just trying to take one shot at a time."
Dufner credited his round to crisp iron play that "put me in positions to have some looks at birdies".
"I hit a lot of fairways, a lot of greens, which gave me a lot of good opportunities," he said.
Spieth, who finished with a share of second at Colonial Country Club in Texas on Sunday, teed off on 10 and followed three birdies in his first six holes with back-to-back bogeys.
He rebounded, however, with five birdies on his inward run.
"I hung in there," Spieth said. "My wedge play was awesome last week and it continued this week."
Meanwhile Johnson, who will defend his maiden major title at the US Open at Erin Hills in Wisconsin in two weeks, got off to a dismal start in this crucial tune-up.
Johnson's six-over par 78 didn't include a single birdie.
Johnson, who had three wins this season before he hurt his back in a fall that forced him out of the Masters in April, teed off on 10 and posted a triple-bogey six at the par-three 16th, where he was in the water.
He also had a bogey and a double-bogey.
It was a tough day, too, for former world number one Jason Day, who had six bogeys and three birdies in a three-over 75.
World number nine Jon Rahm of Spain had a one-over 73 that included a double bogey at the par-four sixth.
Japan's Hideki Matsuyama, who won his first US PGA tour title at the Memorial in 2014, shook off a tough front nine with four birdies coming in en route to a two-under 70.
Matsuyama was among a group of 13 players sharing 13th place that also included five-time major winner Phil Mickelson and Rickie Fowler.
Leading first-round scores on Thursday in the PGA Tour's Memorial tournament in Dublin, Ohio (USA unless noted, par-72):
65 - David Lingmerth (SWE), Jason Dufner
66 - Daniel Summerhays, Jordan Spieth
67 - Justin Thomas, Lucas Glover
68 - An Byeong-Hun (KOR), Sam Saunders
69 - Jamie Lovemark, Nick Taylor (CAN), Matt Kuchar, Brooks Koepka
- Ricky Barnes, Kyle Reifers, Patrick Rodgers, Marc Leishman (AUS),
Keegan Bradley, Kevin Kisner, Phil Mickelson, Pat Perez, Brian Stuard,
Jim Herman, Rickie Fowler, Hideki Matsuyama (JPN), Charl Schwartzel