US Open 2023: Rickie Fowler and Xander Schauffele hit record 62s as Rory McIlroy charges
World number one Scheffler bookended his round with a bogey on the first and last, but found a spark around the turn with five birdies in eight holes to card a creditable 67.
That scored was matched by 2020 US Open champion DeChambeau, who had an eventful round with six birdies and three bogeys.
Local favourite Max Homa, who was born in Los Angeles and holds the course record of 61, is just a shot further back on two under while Viktor Hovland is one under after a round of highs and lows that included a hole-out eagle from 175 yards and a double-bogey seven.
Norwegian Hovland, 25, has come close in the past three majors, playing in the final groups in both last year's Open Championship and last month's US PGA Championship.
Reigning Masters champion Rahm looked largely frustrated with three birdies and two bogeys in his one-under 69.
The Spaniard has a great record in California, with five of his PGA Tour wins coming in the state - including his 2019 US Open victory at Torrey Pines in nearby San Diego.
Jordan Smith is the leading Englishman after shooting a level-par 70 that featured five bogeys and five birdies, while defending champion Matt Fitzpatrick headed to the practice range after signing for a 71.
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