Los Angeles - American Chez Reavie fired an eight-under-par 63 on Thursday to upstage major champions Jordan Spieth and Jason Day in the first round of the PGA Tour Pebble Beach Pro-Am.
Reavie fired an eagle and seven birdies with one bogey on the par-71 Monterey Peninsula course, one of three in use for the tournament along with Pebble Beach Golf Links and Spyglass Hill -- both par-72 layouts.
World number one Spieth, winner of the Masters and US Open last year, opened with a one-under 71 at Spyglass Hill, as did reigning PGA Champion Day of Australia.
"A bit weak," was Spieth's assessment of his round, which included four birdies and three bogeys.
Spieth said a shaky short game led to setbacks on some of the course's easier holes.
"I played the hardest holes on this golf course four under par," Spieth said. "And then I played all the easy ones over par... I'm not quite dialled in with my wedges or with the short game right now."
Nevertheless, Spieth said he wasn't discouraged, with the two courses he considers easier coming up in the rotation in an event in which pros play alongside celebrity amateurs in the opening rounds.
"To actually shoot one under with what I felt like I should have shot today is promising," he said.
Day teed off on 10 at Spyglass had three bogeys and two birdies in his first nine holes. He managed to get under par for the day with two birdies coming in.
Sweden's Freddie Jacobson collected five birdies in one six-hole stretch at Pebble Beach and added two more for a seven under 65 and a share of second. He was joined at seven under by Australian Cameron Smith and American Bronson Burgoon, who both shot 64 at Monterey Peninsula.
England's Justin Rose was among seven players at six under.
Leading first-round scores on Thursday in the US PGA Tour Pebble Beach National Pro-Am on the par-72 Pebble Beach Golf Links, par-71 Monterey Peninsula, par-72 Spyglass Hill (USA unless noted):
63 - Chez Reavie
64 - Cameron Smith (AUS), Bronson Burgoon
65 - Freddie Jacobson (SWE)
65 - Ricky Barnes
66 - Justin Rose (ENG), Dawie van der Walt (RSA), Roberto Castro, Shane Bertsch, J.B. Holmes, Spencer Levin
66 - Jason Gore, Hiroshi Iwata (JPN)
67 - Ryan Ruffels (AUS), Rhein Gibson (AUS)
67 - David Hearn (CAN), Troy Merritt, Kevin Na, Paul Dunne (IRL), Jonas Blixt (SWE), Tom Gillis, Sean O'Hair
68 - Phil Mickelson, Brooks Koepka, Bud Cauley, Steven Bowditch (AUS), Matt Jones (AUS), Thomas Aiken (RSA)