An opening-round 62 left Jon Rahm top of the leaderboard at the Farmers Insurance Open with Rory McIlroy and Seamus Power well off the pace in San Diego.
Rahm hit four consecutive birdies and two eagles as he soared clear. The 24-year-old dropped a shot on the par-three third but picked up shots on four of the final five holes of his round to card a 62 for 10-under and a one shot lead.
England's Justin Rose is a shot behind after carding a clean round of 63, opening with an eagle on the par-five 10th. Also tied for second is American Doug Ghim, who is playing for the first time at the tournament.
He picked up shots on five straight holes on the front nine and went bogey-eagle-par on the closing three.
Scot Russell Knox is one of 12 players tied for 15th on five-under, alongside reigning champion Jason Day from Australia.
Three shots behind that is Tiger Woods, one of a large group who went round in 70.
McIlroy is a shot behind the American on one-under while Waterford man Power had a torrid time at Torrey Pines, reaching the turn on three over and dropping another three shots on the way in to sit tied for 151 on four over.
Both face a battle to make the cut.