World number one Rory McIlroy is four shots off the lead after a carding a three-under-par opening round at the Genesis Invitational in California.
The 30-year-old Northern Irishman, who is back on top of the world rankings for the first time in five years, shot a 68 that included two eagles.
American Matt Kuchar has the clubhouse lead after shooting a seven-under 64.
Tiger Woods, bidding for a PGA Tour record 83rd win, was four under at the halfway stage of his round.
The PGA Tour event at Pacific Palisades in Los Angeles sees nine of the world's top 10 players taking part.