McIlroy is competing in the pro-am event with his father Gerry and will have four-time Pebble Beach victor Phil Mickelson for company over the next three days at Spyglass Hill, Monterey Peninsula Country Club and Pebble Beach.
Matt Kuchar and Julian Suri were in a three-way tie for third after posting matching 66s.
But plenty of serious golf business remains, including world No. 2 Jon Rahm's bid to overtake Johnson atop the world rankings.
Defending champion Jordan Spieth is tied for 23rd place at 5-under after shooting a 66 on Monterey Peninsula.
DJ had eight birdies and one lone drop shot on his round today.
"Kind of the same as yesterday", Johnson said.
At stake on Sunday is a shot at his third victory at Pebble Beach that would strengthen his grip on No. 1 in the world.
"I could do things a little bit better but I had a lot of really good looks at birdie and didn't really make anything".
"I've still had a couple chances to win in recent years, even when I didn't play well there", he said.
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Mickelson was encouraged after his round, which featured six birdies and no bogeys. That's not the reason that I'm out here to play, I've got everything I need.
"But with how I was sort of dejected and wanting to get away from it I was then, to how rejuvenated and optimistic I am now, it feels a lot different that way".
The four-time Major victor used his putter from just off the green and while credited with four putts on the putting surface proper it was five putts with the shortest club in his bag and an unwanted first double of the New Year.
For Gerry McIlory, who worked three jobs at times as his son aspired to golf greatness, there is not much better.
Scoring conditions were so good - everything was good about this day - that 97 out of the 156 players broke par. "I don't know if it's quite as good as it was during that stretch", he said. His dad, Scott, an avid bowler, rolled a 300 game back home in Columbia, S.C. Dustin Johnson also is an accomplished bowler, with a high game of 292.
"It's hard to assess it, it's hard to explain it in words", Rahm said of his rapid ascent that includes four wins worldwide. "I just love everything about it". Mickelson was tied for the lead at one point when he ran off three straight birdies at Monterey Peninsula, though he made only two more over his final 11 holes for a 65.
"I've still got two rounds at Pebble, which is probably my favorite out of the three courses and I really like playing there".
Despite the venue's fame, the event had been mostly ignored by the world's elite in recent years but it has regained its attraction with the top players embracing the pro-am format.
Dustin Johnson has teamed up with future father-in-law, Wayne Gretzky at the AT&T Pebble Beach Pro-Am.
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