Following on from his top ten finish at the European Tour's PGA Championship last weekend, Shane Lowry has moved into contention going into the weekend at the Memorial Championship on the PGA Tour. His first bogey didn't come until the par-4 13th, but he made two more birdies on his way to the clubhouse to get to 13-under for the tournament.
The No. 6-ranked Spieth carded a 6-under 66, tied for third with Daniel Summerhays.
A rock-solid par at the last kept him three clear of 2013 champion Kuchar, who closed out an outward 34 with back-to-back birdies and picked up four birdies in five holes from the 13th, although a blocked tee shot at the short 16th led to his only blemish of the round. They all have a long way to go to get to Dufner.
Dufner's scorecard included five birdies and an eagle.
Dufner's bogey-free round was highlighted by an eagle at the par-4 18th, his ninth hole of the day.
"I felt like I scored the way I played today", Spieth said.
"If I can drive it like this at the US Open, a major where it's so crucial to drive it straight, it should be a good week", said Leishman.
"I'm OK", Dufner said.
Rickie Fowler (8 under): It has been an odd week for Fowler, who shot 70-62-72 over the first three rounds.
But he has not yet missed a putt from inside 10 feet, a feat he credits to recent work with a putting training device that has helped his consistency.
Johnson's round was marred by a triple-bogey at the par-three 16th, where his tee shot found the pond guarding the green, before he compounded his misery by three-putting.
"A lot of luck with it going in", Dufner said.
Daniel Summerhays bogeyed his last hole and shot 69, leaving him five shots behind Dufner. Fowler (66) was another shot behind. Spieth started the back nine with two straight birdies only to follow with two straight bogeys.
"I hate missing cuts", Johnson said.
"I consistently put myself in good spots around the greens and was able to roll a few in".
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.
But the Columbus resident Day lamented just three opening rounds under par in nine starts at Muirfield Village, where he is a member.
Co-leader Dufner has also had a quiet season, with just one top-10, but one would not have known it by the way he dismantled Muirfield Village.
Taking the week off, Jutanugarn replaced Lydia Ko atop the ranking when So Yeon Ryu missed the cut.
Matsuyama was among a group of 13 players sharing 13th place that also included five-time major victor Phil Mickelson and Rickie Fowler.