Combined with Fowler's 65 on Thursday, this marked the first time that three golfers had 7-under rounds in the same Open. He birdied four of his last six holes - he missed two birdie putts of 10 feet and two-putted for birdie on the par-5 seventh - to rally for a 71.
Rory McIlroy will miss the cut, but at least one of his U.S. Open records is safe - 35 consecutive holes without a bogey to start a U.S. Open. Fowler shot a 73 and was still very much in the hunt at a second straight major.
"It was a good display, all my own fault, but a good display of what can happen if you get out of position on this golf course", he said.
The opening round was without Phil Mickelson for the first time since 1993.
And they had even more company.
"It's going to be a really cool day for someone tomorrow", Fowler said.
Day shot a 75 for a two-day total of 10-over 154, ending at 17 the longest active streak of making the cut in the majors.
It sounds as if Erin Hills is becoming more challenging with each passing minute. "So it's just nice to see it come along at the right time". The USGA is providing complimentary bottled water the rest of the week. That's not to say big names and quality players aren't in the mix here in Wisconsin. With about two hours left in the second round, the cut was looking to be 1-over par, which would tie a US Open record.
It didn't for Rory McIlroy, either. His birdie putts for no gimmies, at 12, 8, and 15 feet. 1, 2 and 3 all missed the cut in a major.More news: Alexis Sanchez sprains ankle, may miss Cameroon clash
"I think at the end of the day, it's competitive rounds and get the card in my hand", McIlroy said. "I couldn't possibly shoot any higher than I did". And at this U.S. Open, he showed how a quick recovery is never too far away.
Despite a flurry of late birdies it was not enough to turnaround an erratic round littered with errors and missed opportunities.
Other notable players failing to make the cut included British Open champion Henrik Stenson (147), former Masters winners Charl Schwartzel (147) of South Africa and Australian Adam Scott (147) and double Masters victor Bubba Watson (148).
Wet conditions helped produce low scores in round one, but Casey noticed a difference in difficulty at Erin Hills on Friday.
Casey refused to let the triple get him down and accepted accountability.
"We're in a good spot", Fowler said.
South Africans Thomas Aiken and Ernie Els were 2 under par, with Louis Oosthuizen, Branden Grace and Brandon Stone on even par, all still in contention sas the Open entered the final two days.
Casey made a snowman - a triple-bogey 8 on the par-5 14th - and still broke par with a 71.
"I just played bad golf, man", Day said. "Yeah, it was a bit of a roller coaster".
The Englishman found himself in trouble when he flew his approach out of rough over the green into the deep fescue and needed five more strokes to get in the cup.