He shot 72 and finished at 13 under.
Johnson, who had already had a four-stroke lead, holed out with a nine-iron for his second shot on the par-4 18th.
CHASING: Well, there's really nobody technically chasing as Johnson and Putnam are five in front of everybody else.
"I have high expectations going in every week", Johnson said. "If I play really good golf, I'm probably going to win".
"I hit a lot of great shots in there, had a lot of good looks at birdie". You can't really let up. "For me if helps me identify the things I need to work on - and this week that was my short game".
Five-time major victor Phil Mickelson was four under after two birdies in his last three holes. Pan was set to join the duo after birdies at Nos. Scott Piercy withdrew after nine holes at 5 over. "It seems like it's been a long time even though it's just been six months (since I won)".
"I haven't seen the golf course yet but I'll go there tomorrow and get 18 holes in and we'll see".More news: Multistate salmonella outbreak linked to pre-cut melons
Brandt Snedeker shot his best round this year with a 62 that was one stroke off the course record.
Five-time major victor 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. Johnson said he couldn't tell if the ball went in for a few seconds. "And I made a few bogeys because I struggled with the difficulty around the greens".
Ricky Werenski got to 10 under but bogeyed No. 18 to finish with a 68.
Two-time defending champion Daniel Berger - trying to become the first three-peat champion on the PGA Tour since Steve Stricker won the John Deere in 2009, '10 and '11 - missed the cut by one stroke after shooting 1-over 71, which followed an opening-round 70.
Blaum redeemed a bogey at the first with seven birdies in a 64 and Putnam matched that effort as both seek a first win on the PGA Tour. Berger does not have a top-10 finish in 12 starts this season.
It's no surprise that he enters the U.S. Open as the favorite.
Success! An email has been sent with a link to confirm list signup.
Get prep sports breaking news alerts from the Gwinnett Daily Post staff delivered to your email.