Saunders on Thursday fired seven birdies in a seven-under-par 64 to seize a two-stroke lead.
Saunders on Thursday fired seven birdies in a seven-under-par 64 to seize a two-stroke lead over US Open champion Dustin Johnson and four other players in a round delayed by fog and halted by darkness.
World number three Johnson, who has a chance to topple Australian Jason Day from the top of the rankings with a win this week, had six birdies and a bogey in his 66.
Day was among 48 players still on the course when darkness fell and was even through 16 after four birdies and four bogeys.
Two-time major winner Jordan Spieth was two-under through 16 and world number five Hideki Matsuyama -- who like Johnson could possibly seize the number one ranking with a win, was one-under through 16.
The first round was scheduled to resume at 7 am (1500 GMT), with the second to start shortly thereafter, if predicted rain storms don't intervene.
"(It's) kind of a little bit of a bonus," Saunders said of completing the round, adding that he was "mentally prepared" for the possibility that weather could prevent him from playing at all on Friday.
Saunders, 29, took center stage in October with a moving eulogy at a memorial service for Palmer, who died on September 25 at the age of 87.
While he once may have felt pressure to escape from Palmer's shadow, that's a burden he no longer carries.
"I don't need to compete against my grandfather's career," he said. "Nobody can. Nobody's going to compete. I don't care how many golf tournaments you win, nobody's going to compete in the terms of doing what he did for the game."
While Saunders is playing Riviera for the first time, Johnson is after a win on a course where has come close several times, including a 2015 playoff loss to James Hahn.
Johnson's round was enlivened by a bee sting on the green at the first hole, his 10th of the day. He responded with birdie putts of 24 and 31 feet at the second and third.
"The golf course gave me a little love back after I got the bee sting," said Johnson, who was alone atop the leaderboard at six-under before his lone bogey of the day at the par-three fourth.
"I was just hitting really good golf shots," said Johnson, who was tied with newcomer J.T. Poston, Daniel Summerhays, Brett Stegmaier and Australian Cameron Percy, who birdied 18 for a share of second shortly before darkness fell.
"It's definitely nice to having a later tee time tomorrow because I can get up and kind of see how things are going and we'll know if we're going to play or not," Johnson said.
Five-time major winner Phil Mickelson headed a group on four-under 67. He was joined by Australia's Marc Leishman, Ireland's Padraig Harrington, South Africa's Branden Grace, South Korea's An Byeong-Hun and Americans Billy Hurley, Pat Perez and Kevin Na.