Two-time US Open champion Brooks Koepka has shown glimpses of his impressive major-winning credentials but was scrappy in a round of 74 to drop to two over par.
Two shots further behind, the 2021 champion Jon Rahm saw his challenge falter, having impressed on day one.
Starting the round three off the lead, he followed three bogeys on his first nine with a penal double bogey at the 12th to drop to four over par, with his sole birdie arriving at the fourth.
To compound his frustration, he saw a series of birdie chances slide by during his closing holes before a bogey at the last left him seven shots off the lead.
“I’m too mad to put it into perspective,” he said afterwards.
At least Rahm made the cut.
DeChambeau was a shadow of the player who stormed to victory at Pinehurst last June as his title defence faded with a whimper.
Sweden’s Ludvig Aberg and England’s Tommy Fleetwood are also heading home, finishing at eight over and nine over respectively.
And Ireland’s Shane Lowry closed on 17 over par, after a round which featured a penalty shot for picking up his ball without marking it on the 14th green.
“Maybe my mind was somewhere else,” laughed Lowry when recounting the bizarre incident to BBC Sport. “It’s one of the stupidest things I’ve done.”
Six-time runner-up Phil Mickelson, who suggested this may be his last US Open, missed a birdie putt on the last to to end up on the wrong side of the cut line.
Meanwhile, France’s Victor Perez had a hole-in-one at the par-three sixth and a triple-bogey eight in a level-par 70 that kept him at one over and inside the top 10.
