Kevin Streelman and Beau Hossler enjoyed flawless starts to set the early pace at the Pebble Beach Pro-Am, while former world number one Rory McIlroy impressed to be within striking distance.
All eyes were on Northern Irish star McIlroy as he made his first PGA Tour appearance since the BMW Championship in September.
But McIlroy was upstaged by Streelman and Hossler, who produced 7-under-par 65s to earn a share of the one-shot lead in California on Thursday.
McIlroy ended the opening round three shots adrift after American pair Streelman and Hossler carded bogey-free rounds.
Back-to-back ! @McIlroyRory goes out in under. pic.twitter.com/Zt7x7Z37BP
— PGA TOUR (@PGATOUR) February 8, 2018
Playing at Spyglass Hill, Streelman recorded seven birdies without dropping a shot, while countryman Hossler also holed seven birdies at Pebble Beach to be clear of Matt Kuchar, Aaron Wise and Julian Suri.
Four-time major champion McIlroy — who already has two top-three finishes on the European Tour this year — made a bright start with a first-round 68.
At Spyglass Hill, McIlroy had six birdies and two bogeys to be level alongside the likes of Jon Rahm and Shane Lowry.
McIlroy's pro-am partner this week is his father Gerry.
Like father, like son. #QuickHits pic.twitter.com/s8NsHAZ69S
— PGA TOUR (@PGATOUR) February 8, 2018
Former world No. 1 and 2015 PGA Championship winner Jason Day is a shot further back following his 3-under-par 69.
Day, who broke his 20-month winless streak at Torrey Pines a fortnight ago, tallied five birdies and two bogeys.
Three-time major winner and American star Jordan Spieth had a birdie and a bogey to be even par following his 72.
Major champions Adam Scott and Ernie Els struggled after the pair both posted 77s to be 5 over heading into the second round.
Meanwhile, NHL legend Wayne Gretzky produced one of the highlights of the day.
"You miss 100% of the shots you don't take." - @
wayneGretzky#MustSeeMoments pic.twitter.com/dY5J6Y3Jvm
— PGA TOUR (@PGATOUR) February 9, 2018
Playing alongside world number one Dustin Johnson, Gretzky drained a long birdie putt on his first hole of the round.
Packers quarterback Aaron Rodgers — who has teamed up with Jerry Kelly — also nailed a birdie