McIlroy joked earlier in the week that anyone who couldn't hit such wide fairways "might as well pack your bags and go home".
From there, Fowler's major fate sagged, his last nine majors crammed with three missed cuts, four more finishes outside the top 30 and zero top 10s.
Fowler took advantage of Erin Hills' four par 5s, all of which he birdied, including two which came back-to-back as Fowler registered three straight birdies as he made the turn.
"It is always cool to be part of some sort of history in golf".
Fowler is bidding to become the seventh first-time major victor in a row with in Wisconsin this week.
Paul Casey and Xander Schauffele tied for the lowest round of the afternoon wave with 6-under 66s. Many viewed Day as a favorite because of his driving prowess, but he finished his opening round with two triple-bogeys and five bogeys.
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"I just did a good job, knew I needed to drive it well, and from there [I was] just able to continue to swing well and hit good shots and roll a couple in".
"And I did well today, but I probably missed a few par putts, or I'd be 1-under or 2-under after a really good start".
McIlroy has played just six tournaments this year after battling through a rib injury but said pain was not to blame for his performance on Thursday. "Just hitting the fairways has made it a little easier and that's definitely something that makes a difference out here".
The misery started after his second shot from 178 yards landed just off the green, about 29 feet from the hole.
Day meanwhile was left sliding towards an early exit after a calamitous seven-over-par 79.
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European Tour player Ormsby joined compatriot Nick Flanagan at three-over and tied for 102nd place.
Former US Open champion Ernie Els chose the 20th anniversary of his last victory in the tournament to remind fans that he is not quite ready to be put out to grass.
The 47-year-old South African has struggled this year; he hasn't finished better than 35th. I hope the guys got out okay.
It took him to 1-under par after his first six holes - two shots off the lead.
According to Terry Sater of WISN-TV in Milwaukee, the NTSB is gathering information about Thursday's blimp crash.
Players and fans looked on in disbelief as the aircraft fell from the sky near the venue.
A spokesperson for Airsign, an aerial advertising firm based in Florida, said its blimp was involved in the incident, and told ABC News the pilot suffered nonlife-threatening burns and will be "OK". "I felt awful for the people inside", golfer Jamie Lovemark said at a news conference.
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Monica, 42, and Billue, 58, are being remembered as having had an "unwavering commitment to their job and their love of family". Christopher Monica had been employed with the Georgia Department of Corrections since 2009, according to the department.
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