England's Paul Casey was one shot clear after play at the Frys.com Open was suspended for the night at CordeValle Golf Club.
The start of the second round had been delayed by almost two and a half hours due to fog and it will now resume on Saturday.
When play was halted Casey was still in the lead at eight under following a seven under par 64, though Troy Matteson, Ernie Els and Briny Baird had all inched closer.
Els was tied for second with Bud Cauley, who finished with a five under par 66, but could have tied for the lead only to miss an eagle putt on the par five 15th.
He also had a putt to tie the lead on the par three 16th when the horn blew.
Els opted to finish the hole but missed the eight footer and had to settle for par.
Matteson, meanwhile, was six under and Baird five under when play was halted.
Former World Number One Tiger Woods made a marked improvement on his first round with a three under par 68.
Casey sunk eight birdies and one bogey just weeks after suffering a foot injury.
He said: "It's the first time I've been on the golf course since making progress with the foot and the toes, and it was night and day.
"Suddenly a little bit of confidence, the ball-striking is coming back.
"It's nice to look up and know that the golf ball is actually going in the direction that I wanted it to go in which hasn't happened in a really long time."
