Three shots behind him at Silverado Resort's North Course is Jackson Koivun and Russell Henley, who makes his Ryder Cup debut in two weeks. Henley dropped a few shots on his back nine and shot 68.
Koivun, the No.1 player in the World Amateur Golf Rankings, is in contention after a 66 that included six birdies, an eagle and two bogeys.
Next was J.J. Spaun (68), the US Open champion who also will be at Bethpage Black, five shots behind.
Canadian, and round one leader, Mackenzie Hughes shot a 74 to be tied for seventh at seven under, with six others.
Griffin enjoyed two birdies on the front nine but finished strongly with birdies on 12, 15, 17 and 18.
"I wouldn't even say my mindset's been Ryder Cup. I've been pretty focused on this golf tournament," Griffin said.
"Without a doubt off the golf course hanging out with the guys and stuff there's been some Ryder Cup presence, but once I get on the first tee I'm thinking I'm trying to play well here."
Griffin, one of four Ryder Cup rookies along with Henley, Spaun and Cameron Young, was at 14-under 130.
Scottie Scheffler had a few more birdies than his opening round but his ho-hum 68 left him eight shots behind. The world No.1 hasn't finished worse than eighth since March.
Some two hours after his round, Griffin was a lone figure on the practice green on a gorgeous late summer day in Napa as he worked on his putting.
"This week I'm trying to literally do the same stuff I'm doing," Griffin said.
"I'm trying to stay confident, stay motivated and keep the pedal down."
Karl Vilips (70) is the only Australian left in the field, in a tie for 61st at one under, after compatriot Harrison Endycott (75) finished three over and missed the cut.
With AAP.
