Johnson holed out for an eagle and nabbed six birdies as he built a 10-under par total of 130 at TPC Southwind in Memphis, Tennessee.
"I feel like I'm playing really well," said Johnson, who lost the number one ranking to Justin Thomas last month after reigning for 64 straight weeks.
"I'm swinging the club well. I know if I can drive it in the fairway I'm going to give myself a good look for birdie. I felt like I did that pretty much all day.
"I hit a lot of great shots in there, had a lot of good looks at birdie." Johnson opened with a birdie at the 10th. After bogeys at 12 and 13 he bounced back with birdies at 14 and 16.
He jump-started his round with an eagle at the first, where he holed out with a wedge from 111 yards.
Johnson's approach at the second left him less than a foot for birdie, and he added birdies at three, six and nine -- and needed only 24 putts in the round.
"I'm rolling it down the line I'm looking," Johnson said. "If I can get a good read and good speed, they're going to go in." Blaum had seven birdies in a six-under 64 and as did Putnam as they shared second on nine-under 131.
Snedeker, coming back this season after injury sidelined him for much of 2017, said it was encouraging to see his work paying off.
"Until you start seeing results, you start questioning what you're doing," he said.
"You need to see these positive days, where it's, 'OK, I am doing the right stuff, and it's coming around. I'm not losing my mind.'" Five-time major winner Phil Mickelson, trying to build momentum for a run at the US Open title that has so long eluded him, followed up his first-round 66 with an even par 70.
"It's tough to get the ball on the green if you don't drive it in the fairway," Mickelson said. "And around the greens it's tough because the rough is challenging. I made a few bogeys because I struggled with the difficulty around the greens.
"I didn't really have it today, but I was able to close out the round with a couple of birdies and get it back to even and I'm in a decent position.
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