Rickie Fowler fired 10 birdies in a US Open record low round of 62 on Thursday before Xander Schauffele matched it minutes later to share the lead at Los Angeles Country Club midway through the first round.
Fowler, fighting out of a slump that saw him miss the past two US Opens, had 10 birdies and two bogeys and surpassed the previous record low round of 63.
That had been achieved six times in the US Open, most recently Tommy Fleetwood's seven-under effort at Shinnecock in 2018.
Schauffele, the 2021 Olympic champion playing two groups behind Fowler, had eight birdies without a bogey. He had a 27-foot birdie putt at his final hole, the par-three ninth, but left it four feet short.
With afternoon starters on the course, the eight-under-par leading duo were three strokes clear of a group led by world number one Scottie Scheffler.
Scheffler was joined on 67 by former US Open champion Bryson DeChambeau, South Korean Kim Si-woo and France's Paul Barjon. Barjon, playing in his third US Open, was eight-under through 17 holes but bogeyed his final hole, the ninth.
Fowler, a former world number four who fell to as low as 185th after missing 18 cuts in 28 events in 2021 and 2022, got his charge going early with a six-foot birdie at the 10th hole.
He bounced back from a bogey at 11 with birdies at 12, 14 and 16, rolling in putts of 18, 11 and 13 feet. After a bogey at 17, he birdied three straight, launching the run with a 15-footer at the 18th.
He got up and down for par from a greenside bunker at the fourth before a birdie at the sixth, and birdied the par-five eighth despite finding himself in the barranca below the fairway off the tee.
He two-putted for par from 60 feet at the par-three ninth.
"I knew it was close, I wasn't sure of the exact number," Fowler said of the low-round record. "I just tried to keep moving forward."
Both Fowler and Schauffele matched the lowest round recorded in any major championship -- Branden Grace's 62 in the third round of the Open Championship at Royal Birkdale in 2017.
Overcast skies and intermittent mist greeted early starters on LA Country Club's North Course, which is hosting the US Open for the first time.
The benign conditions made for some impressive scoring, but the morning was not without its frustrations.
Masters champion Jon Rahm, struggling to build momentum, battled his way to a one-under par 69 that included three birdies and two bogeys.
Matthieu Pavon energized the crowds as he became the first French player to make a hole-in-one at the US Open, acing the 124-yard par-three 15th.
The hole, which can be set up to play at around 80 yards, was playing closer to its scorecard distance of 124 on Thursday. Pavon's tee shot landed several feet beyond the pin with just enough spin to trickle back into the hole.
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