Sam Saunders (64) leads Genesis Open by two after partial first round

Sam Saunders, by his own admission, never expected to shoot a round like he did at the Riviera Country Club in the Genesis Open on Thursday.

And it’s understandable considering it was his first competitive round there and only the second time this week he has played 18 holes.

“You never really expect to go out and shoot 64 and be leading after the first day,” Saunders said. “I would like to get to that position, but … I don’t think I’m there yet, or at least my track record doesn’t prove that.”

Saunders, whose name has always carried an asterisk as Arnold Palmer’s grandson, has never won a tournament in 79 starts on the PGA Tour. On Monday, he stopped playing after 12 holes because of a rib injury. Clearly, all is fine now.

Saunders holds a two-shot lead with 48 players still on the course when the first round was suspended because of darkness at 5:34 p.m. The day started with two fog delays lasting a total of 75 minutes.

Saunders had seven birdies and no bogeys in his best-ever round on tour. He made two putts of more than 20 feet (24 feet on No. 12, and 21 feet on No. 7) and made three birdie putts of less than three feet.

Play on Friday is tenuous at best and non-existent at worst. PGA Tour officials will try to get a little play in before the winter storm, which is expected to drop between three and five inches of rain, is at its height around midday.

The completion of the first round is scheduled to start at 7:10 a.m., with the players required to be on the course at 7. The second round also is supposed to start at 7:10 a.m.

Dustin Johnson, J.T. Poston, Daniel Summerhays , Brett Stegmaier and Cameron Percy were two off the lead at five under. Johnson is a U.S. Open winner and Poston got in the tournament by winning a Monday qualifier at Industry Hills. Prior to the Genesis, Summerhays was winless in 173 Tour starts. Percy, who finished 10^th at Pebble Beach last week, is winless starting his 104^th tournament.

Johnson, who started on the back nine, birdied six of the first 12 holes before a bogey on the fourth hole.

“I played good,” Johnson said. “I hit a lot of great shots. Overall it was a really good day. I felt I drove it pretty well, especially the first 13 holes. I played really, really solid.”

Johnson seems content with Friday’s disruption of play.

“It’s definitely nice having a later tee time because I can get up and see how things are going and we’ll know if we’re going to play or not,” Johnson said. “The other guys are going to have to be out there in the morning.”

Poston started his round with an eagle on the first hole and followed it up with a bogey.

“The bogey on two was just a bad tee ball and kind of got stuck behind a tree and didn’t have much,” said Poston, 23, whose best finish in 2017 is 34th at the CareerBuilder Challenge. “Other than that, it was a pretty solid round of golf. Pretty happy with it.”

Summerhays played a bogey-free round to shoot his 66.

“My iron play was a little bit better, which I’ve been working on a lot,” Summerhays said. “I was able to roll a few putts in. Overall, really solid.”

There are eight players who finished at four-under 67, including Phil Mickelson, Padraig Harrington and Pat Perez.

“I didn’t putt real wel,l but I made my 40-footers and I didn’t make my five-footers,” Perez said. “I’m usually pretty good on these greens from inside 10 feet and I really didn’t make the ones I wanted to and I made two really long ones.”

Perez has been playing professionally for about 20 years, almost exclusively on the Tour. He won the Bob Hope Desert Classic in 2009 and didn’t win again until the OHL Classic at Mayakoba in November.

One of the most interesting nine-hole stretches belonged to Sahith Theegala, the only amateur in the tournament. The Pepperdine player from Chino Hills qualified Monday when he won the Collegiate Challenge.

Theegala started on the 10^th hole and went par, eagle, bogey, birdie, birdie, bogey, birdie, par, birdie. He was at three under after 12 holes at darkness.

Jhonattan Vegas (through 14), John Huh (12) and Jason Kokrak (12) were the low scorers at four under who did not complete their round.

Jordan Spieth, winner last week at Pebble Beach, was two under through 16 holes when play was halted.

john.cherwa@latimes.com

Twitter: @jcherwa