The start of the second round had been delayed by almost two and a half hours due to fog and it will now resume in the morning.
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 woeful first round when his two-over-par 73 put him in danger of missing the cut.
However, the American sunk 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."
Woods made six birdies and three bogeys and he is seven shots off the lead.
He said: "It's always a progression.
"You've got to do it on the range at home and got to do it on the golf course and at home and eventually here and down the stretch and then in major championships and win those bad boys."
There were also signs of consistency from Woods who added: "I've come off of injuries before in the past, but it's always been the same swing.
"It's pretty easy to come back to that. But when you're implementing changes, it's nice to have more competitive reps to fall back to because as of right now, I haven't had that many competitive reps with Sean [Foley].
"I don't like missing cuts, period. If I miss the cut, that means you can't win the tournament on the weekend.
"I've got a shot at it this weekend."