Beau Hossler, who keeps showing up on leaderboards in his rookie season, had a 66. The group at 67 included Lucas Glover, while Jason Day was among those at 68.
Many of the other top players struggled.
Justin Thomas, in his debut as the No. 1 player in the world, was trading birdies and bogeys and was making progress until he hit his approach out-of-bounds on the par-5 seventh hole and made double bogey, sending him to a 72. Also at 72 was Dustin Johnson, who made nothing but pars on the back nine and failed to birdie any of the par-5s.
Rory McIlroy played the par-5s in one-over and shot 74. Phil Mickelson was four-under through eight holes until a double bogey on No. 9, and then had four bogeys over his last six holes for a 74. Jordan Spieth shot 75, hurt by two double bogeys on the front nine. He went from a fairway bunker into the water on No. 6, and then went some 25 yards beyond the green on the par-3 eighth for another double bogey.
Matsuyama’s big run began after a sluggish start to the back nine on a muggy, humid day that left Muirfield Village soft, particularly with a burst of heavy rain late Wednesday. He chopped his way out of the nasty rough on the 10th and 11th holes, both times making bogey.
And then he couldn’t miss.
It started with an 18-foot birdie putt on No. 13. He followed with a wedge to tap-in range on the 14th and another wedge to 2 feet on the par-5 15th. After a 12-foot birdie putt on the par-3 16th, he was in the middle of the fairway when his wedge landed beyond the hole and spun back into the cup.