The world number six was one of just 32 players to complete their second rounds due to persistent fog, but the testing conditions did not disrupt the American as he carded a round of 65 that saw him move onto ten-under-par for the tournament.
The 23-year-old's round included eight birdies and just one dropped shot as he moved into the clubhouse lead, although he is joined at the top of the standings by compatriot Derek Fathauer, who still has one hole to play of his second round.
Spieth, who is looking to claim his ninth PGA Tour title this week, was pleased by his performance on Friday, although he knows there is still a lot of golf to play before he can start thinking of overall glory.
"I didn't feel any nerves out there, even though I knew I was toward the lead, just because so much could happen with three courses," he said. "The first two rounds, it's been easy. Tomorrow might feel a little different.
"But in my opinion, I'm at 10 under now. If I can try and just make two [birdies] a side at Pebble Beach each time, and make up for the bogeys with maybe another birdie, it may be good enough."
World number one Jason Day is a shot off the pace on nine-under, although he still has six holes to play of his second round, while Patrick Reed and Seung-Yul Noh are two shots further back.