The American defending champion followed up his three-over 75 with a 73 as he failed to reach the weekend at Erin Hills.
He three-putted on No. 13.
Lurking at five under was a pack including young South Korean Kim Si-woo, who recovered from an early bogey by stringing together three straight birdies through the turn on the way to a two-under 70.
"It's still golf, you've got to make some putts", said J.B. Holmes, who is one shot off the lead.
Were they just not as sharp as they normally would be for a major?
As for why Johnson, McIlroy and Day struggled, one possible reason is that all have battled injuries or personal situations over the first half of the season that may have kept them from being tournament-ready.
The greens, predictably, had become quicker in the scorching sun and the pins, even more predictably, were not as generously set.
Brendan Steele hits a drive on the fifth hole during the second round of the U.S. Open golf tournament Friday, June 16, 2017, at Erin Hills in Erin, Wis.
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KEY STATISTIC: The cut, at 1 over, tied a U.S. Open record set in 1990 at Medinah.
The final pairing of Casey and Harman are scheduled to tee off at 2:29 p.m. (1925 GMT), but a forecast calling for the possibility of thunderstorms could disrupt third-round action. Those were the only hiccups he had, and he finds himself poised to make noise on moving day.
Casey carded an eagle and six birdies for a six-under-par 66 while Schauffele, the 23-year-old world number 352 also carded a 66.
Discussing his woes at the long 14th, Casey added: "It was all my own fault, but a good display of what can happen if you get out of position on this golf course, which is what I did".
McIlroy's playing partner and former world No 1 Jason Day finished nine over following a 75.
He never would have guessed it. "I wasn't thinking too much about 8 under", he said through an interpreter. "And unfortunately, this didn't pan out".
It didn't for McIlroy, either.
After the Travelers, McIlroy will take a week off and then play in the Irish Open, the Scottish Open and the British Open in consecutive weeks. If only he had hit the fairways.
Fleetwood, six years Casey's junior, continues to impress in only his second U.S. Open tournament. And even that was frustrating. Reavie birdied five of his first seven holes, and eight in all Friday, to surge back into contention. But he missed a pair of 10-foot birdie chances in that stretch, and one of the birdies he made was a two-putt from 20 feet on the par-5 seventh.
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"It will be just fine", said Fowler, who plays in the third-to-last group on Saturday.
After tying for a distant second at the 2014 U.S. Open at Pinehurst No. 2, Fowler missed the cut in his last two U.S. Open starts.
Casey then reignited his charge birding his eighth hole and ended the run with a "3" at his 12th.
The U.S. Open is hailed as the most hard tournament in golf. "I think the more rounds I can play, I'm hopefully going to get rid of all that stuff and hopefully strip it down to what you saw the last six holes".
His schedule will pick up immediately. "A run of three bogeys in a row - from the 11th - derailed Fowler".
"It is going to be great as I've never done this before", he said looking ahead to the weekend. That's been the case all week at Erin Hills.
Health officials say E. coli bacteria have been found in a drinking water station at Erin Hills golf course where the U.S. Open is underway, but there have been no reports of illness.
"Being out of position off the tee does not help", he said.
As for Johnson? His second son was born Monday and Johnson was headed to California to spend time with his family, change some diapers and presumably work on his putting.
Champions Trophy 2017: Pakistan stun England to reach final
India plays Bangladesh on Thursday at Edgbaston in the other semifinal match with India the clear favorite - but so was England. England were not shot out here by unplayable balls, rather they were ground down by their own insecurities.
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