Johnson shook off an opening bogey to make five birdies as the world number two shot a four-under par 67 in the afternoon at Liberty National to move to 12-under for the tournament.
"I drove it really well," Johnson told reporters, pleased to be playing against the backdrop of New York City across the Hudson River.
"You've still got to hit the shots and right now I feel like I'm swinging it really well.
"I've got a lot of control with the golf ball and hitting a lot of really nice shots and rolled in a couple putts today which is nice, but still feel like I left quite a few out there."
Spieth dropped in eight birdies against a single bogey for sparking 64 in the morning for the early lead and ultimately outright second place in the opening event of the FedEX Cup playoffs.
"The game feels good," Spieth said.
"I just made more putts today. I found myself in some easier locations on the greens to be able to knock some mid-rangers in, but I thought the course setup may have been a little bit easier."
But the former world number one knows there is work to be done after struggling on weekends this season, including last week when he shot a 77 on Saturday and failed to make the 54-hole cut at the Wyndham Championship.
Another stroke back were Northern Ireland's world number three Rory McIlroy (68), England world number four Justin Rose (68), South African Louis Oosthuizen (65) and Americans Andrew Putnam (64) and Wyndham Clark (66).
McIlroy was originally assessed a two-stroke penalty at the 14th hole when he touched sand in a bunker he thought was a stone, a rules violation. Officials later reversed the ruling.
"They got the (U.S. Golf Association) involved," McIlroy said later.
"They sort of went back and forth a little bit, and then ... in a way, it came down to me and said, 'okay, are you comfortable telling us you didn't improve your lie,' and for me, I am comfortable saying that."
The game's top ranked player, Brooks Koepka, was nine strokes off the lead after a 69, but Australian Jason Day and Rickie Fowler were both on level par and failed to make the cut, which was set at one-under.
World number five Tiger Woods withdrew from the tournament on Friday morning because of a stiff back.
(Reporting by Gene Cherry in Raleigh, North Carolina, editing by Nick Mulvenney)