Shane Lowry proved the best of the Irish and the only one of the starting quartet to make the cut, reaching the half-way stage just inside the cut mark on one over par.
Day, who had made the cut at every major since the 2012 PGA Championship, followed up his opening round 79 with a 75, leaving the Australian anchored near the bottom of the leaderboard at 10-over.
"It's still golf, you've got to make some putts", said J.B. Holmes, who is one shot off the lead.
"It's pretty frustrating when I got here Friday, put a lot of work in - not a lot, but I tried to pace myself", Day said. It was a bit of a roller coaster.
No fewer than 44 players ducked under par in the first round, and as the second round unfolded on Friday, the 7,839-yard layout continued to give up birdies freely. Hadwin tied a U.S. Open record when he made six straight birdies, from the 18th hole through the fifth hole. "I was trying to stay out of the way of Rosey".
Paul Casey produced a brilliant fightback to remain in contention for a first major title as former champion Rory McIlroy missed the cut in the US Open for the second year running. But on Friday, after running off 28 relatively stress-free holes without a bogey, the mojo suddenly left, and Fowler found himself scrapping and scraping so as not to lose too much ground. I got off to a good start but it sort of caught up with me as the round went on.
Westwood had bogeyed the third and fifth before a superb tee shot on the 239-yard sixth - which played as the most hard hole on Thursday - set up a birdie from 18 feet.
On top of that, he faced a 8:37 a.m. start time for Saturday's third round in the U.S. Open. It should be noted, though, that Colonial plays to a par of 70 versus the par 72 we're seeing at Erin Hills.
Defending champion Dustin Johnson (+4), Rory McIlroy (+5) and Jason Day (+10) will all miss the weekend after their struggles. "I didn't score and then I hit a couple loose shots off the tee that cost me my day".
"You won't get a better day for scoring", Johnson said wistfully during the long walk to sign his card.
McIlroy was playing just his seventh tournament of 2017 due to a rib injury.
But the late birdie spree was not enough to lift McIlroy to safety as the exit door loomed.
RIDE 'EM COWBOYS: Jordan Niebrugge wore an orange shirt for the second round at the U.S. Open, switching to a colour he usually dons on Sundays.
"If you look at the golf course and you even talk to me, Jason or Rory, this course sets up ideal for us", he said. Then he recovered by making birdie at five of his next six to get it back under par on the day.
"It is going to be great as I've never done this before", he said looking ahead to the weekend.