Johnson produced a blemish-free round to burst through the congestion at the top of the leaderboard and head namesake Dustin, Matt Kuchar and Jordan Spieth by three strokes.
Behind them were Webb Simpson and Michael Thompson at nine under, with only two of the 30-strong field over par.
Johnson was one of eight players all within a shot of each other at the top of the leaderboard after the opening day, but he moved clear in serene fashion.
He picked up a shot at the fourth, then birdied four straight from the sixth, eventually carding seven birdies in his round.
"The more I get my feet here, the more I walk these grounds, the more comfortable I become," Johnson told pgatour.com.
His 66 was matched by defending champion Dustin Johnson, who carded nine birdies against two bogeys to head the chasing pack alongside Kuchar and Spieth.
Scotland's Martin Laird was the leading European, sitting in 19th at three under par.