The defending Olympic gold medalist is scheduled to represent the United States in Paris in August.
"Yesterday was a tough day, probably the toughest I've had in my 17 years as a professional golfer."
McIlroy's three bogeys in the final four holes opened the door for DeChambeau, who made a brilliant up-and-down on the 18th to seal victory.
Kiwi Ryan Fox carded a six-over 76 to sit 18 shots off the lead.
The golfing legend said it 'may or may not be' his last US Open.
Ryan Fox lies one shot outside the projected cut and eight behind co-leaders Patrick Cantlay and Rory McIlroy.
Ryan Fox is eager to emulate Campbell's 2005 heroics.
Scot Robert MacIntyre held on for his maiden PGA Tour win.
The eight-shot turnaround has him tied for second behind Scot Robert MacIntyre.
Ryan Fox has kept the momentum going from his strong start in Ontario.
Ryan Fox is level with world No.2 Rory McIlroy after the opening round.
Scottie Scheffler was arrested en route to play the second round of the major earlier this month.
The American withdrew from the Charles Schwab Challenge with illness.
The death has sent shockwaves through the golfing world.
Fox carded five birdies during an impressive second round.
Scottie Scheffler tried to drive around traffic congestion, en route to the second round of the PGA Championship.
The American needed a birdie on the 18th to avoid a playoff with Bryson DeChambeau.
The Americans are tied at 15-under overall at Valhalla.
The world No.1 arrived less than an hour before his tee time directly from a Louisville police holding cell.
The American said the incident was due to a misunderstanding with regards to traffic flow.
