Fox shot a 3-over 73 for the second straight day, which left him at 8-over for the tournament.
It did not take long for the renowned Oakmont Country Club to bite Fox, who had a double bogey at the third yesterday, following pars at the first two holes.
The Canadian Open winner then showed a glimpse of his talent with birdies at four, five and six to get back to 4-over.
His tee shot on the par-3 sixth, in particular, was exceptional, as he hit the ball to within a foot of the hole, but that was as good as it got for Fox, as he dropped a shot on the seventh then posted a second double bogey of the round at the par-4 ninth hole.
He steadied on the back nine, dropping just one shot, when he bogeyed the 15th hole.
Sam Burns moved closer to a major breakthrough as he held a one-shot lead over Australian Adam Scott, who turned back the clock to enter the mix, and J.J. Spaun after the third round of the US Open.
Burns and Spaun took turns trading or sharing the lead for much of the day, but it was the former who finished in front with a one-under-par 69 that brought him to four under on the week at the major that is considered golf’s toughest test.
A five-time winner on the PGA Tour who lost to Fox in a playoff last week in Canada, Burns was inconsistent off the tee but managed to lean on other aspects of his game to move into the driver’s seat at Oakmont.
"When I got out of position I feel like I did a good job of getting myself back in the fairway, having a wedge or short iron in my hand and giving myself a chance for par," said Burns.
"I was able to convert some of those and kind of kept the momentum going. So that was kind of key to the round today."
Burns dropped into a three-way share of the lead with Spaun and Scott after missing a six-foot par putt at 16 but never wavered and delivered a bounce-back birdie at 17 after stuffing his approach seven inches from the hole for a tap-in birdie.
Not to be outdone, playing partner Spaun birdied the same hole from 13 feet to end his string of 12 consecutive pars and grab a share of the lead before an errant tee shot at the last led to a closing bogey for a 69.
Scott, the 2013 Masters champion who is playing his 96th consecutive major, missed several birdie putts but converted three on the back nine for 67, equalling the low round of the day and will play in Sunday’s final pairing with Burns.
For Scott, whose lone major came at the 2013 Masters, a win on Sunday would set the record for longest time between a player winning his first and second majors, something that is not lost on the 44-year-old Australian.
"Everyone out here has got their journey, you know. Putting ourselves in these positions doesn’t just happen by fluke. It’s not easy to do it," said Scott.
"If I were to come away with it tomorrow, it would be a hell of a round of golf and an exclamation point on my career."
World number 14 Viktor Hovland (70) was alone in fourth place and three shots off the pace.
LIV Golf’s Carlos Ortiz was enjoying a rather stress-free trip around the notoriously treacherous Oakmont layout until a closing bogey but still signed for a 67 that left him at even par on the week and alone in fifth place.
Fellow LIV player Tyrell Hatton (68) was a further shot back in sixth place with South African Thriston Lawrence (70).
