Rory McIlroy was left to rue two costly double-bogeys as he slipped six strokes off the early lead at the AT&T Pebble Beach Pro-Am, as world No 1 Scottie Scheffler made a slow start.
McIlroy carded an eagle and six birdies during the opening round of his title defence at Spyglass Hill, one of two courses used at the event, but made three-putt double-bogeys on consecutive par-threes on his way to a four-under 68.
The five-time major winner was ranked outside the top 70 in the 80-man field for putting after his double-bogey woes, which left him outside the top 25 on the leaderboard as Ryo Hisatsune set the pace.
Hisatsune birdied each of his last three holes to close a bogey-free 62 at Pebble Beach, with a birdie, an eagle, and a par-four to finish the round.
Sam Burns and Keegan Bradley are tied in second with bogey-free 63 after the day's play, thanks to Burns' glorious 17th-hole eagle to level the score.
McIlroy - beginning on the back nine in benign conditions - opened with successive birdies and holed out from a greenside bunker to eagle the par-five 13th, before getting up and down from the sand to pick up a shot at the driveable par-four 17th to turn in 31.
The world No 2 was unable to take advantage of the par-five first but rolled in from 15 feet at the next to move to six under, only to see his momentum abruptly halted with a three-putt double bogey from eight feet at the par-three third.
McIlroy responded with a stunning approach into the par-four fourth, setting up a close-range birdie, but three-putt from five feet to rack up another double-bogey at the par-three fifth.
The Northern Irishman was unable to convert good birdie looks at the seventh and eighth but found one on the par-four ninth, his final hole of the day, holing from 14 feet to finish a frustrating round strongly.
Scheffler, on the other hand, finished the day down the standings and out of contention after a frustrating three-bogey 72 left the world No 1 flailing.
"I feel like typically I'm good at scoring and today I felt like I didn't score at all," Scheffler said.
"Like anything that kind of went wrong seemed to be going that direction and I just felt like I scored poorly. I actually feel like I'm playing pretty well, [it was] just one of those days."
"I guess the challenge [at Pebble Beach] is making a bunch of birdies. I'm looking at the leaderboard on behind you right now and it looks like 7 under gets you in the top-10, so scores are pretty low.
"When you're playing later in the day it can be tough to hole putts on these greens."
Justin Rose finished the day on a 69, one behind fellow Brit Harry Hall. Swede Ludvig Aberg, though, continued his early season struggles with a seven-bogey 75 in another round to forget.
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