The Americans dominated the second day's play outside Chicago and will head into Sunday's singles matches 10-6 ahead, although Europe slowed their momentum slightly by winning the final two fourballs contests.
The Europeans also threatened to take a third fourballs point as Paul Lawrie and Nicolas Colsaerts, having trailed for much of their match against Johnson and Matt Kuchar, pulled level with two holes to play.
Johnson dashed their hopes as he rolled in a putt of more than 20 feet for a birdie two on the 17th and, with the last halved, that effectively secured a point for the hosts.
Johnson said: "It was great. My man, my partner here, Matt, he kept us in it all day.
"I pitched in a few holes here or there, but not too much. I was definitely riding on his back for most of the day.
"And then I hit some good shots on the back nine, and then obviously that putt on 17 was one of the best putts I've ever made.
"It's probably the loudest roar I've ever heard, especially in this situation."
While the US will head into the final day as firm favourites to regain the Ryder Cup they lost two years ago, they will not take anything for granted.
Europe led by the same scoreline heading into the singles at Brookline in 1999 but were memorably overhauled by the Americans.
Kuchar said: "It's singles tomorrow [Sunday]. We've got a nice lead but there's 12 points up for grabs. There's still a lot that can happen.
"There's a lot of memories from '99, and I think we have to know that sort of deficit is 'overcomable'.
"We have to go out and still play some really good golf and make sure that we don't let a comeback like that happen to us."