Yet while Fowler and Casey thrived, defending champion Dustin Johnson, world number two Rory McIlroy and world number three Jason Day - three big-hitters who had been tipped to thrive - all had a day to forget.
Sergio lurking: Masters champion Sergio Garcia meanwhile was lurking five off the lead after a two-under-par 70.
Pardon the gallows humor. All the while, another player in his group, Hideki Matsuyama, was busy shooting his own 65.
McIlroy, the reigning FedExCup champ, fared slightly better.
A bogey on the par-four 12th was followed by a birdie on the 13th to leave him at 6-over through four holes.
On the longest course ever for a major, the cut was the lowest at the U.S. Open since 1990. In fact, eight of the top 12 golfers in the world missed the cut, a first in OWGR history dating back to 1986, according to Bob Harig.
Rory McIlroy will miss the cut, but at least one of his US Open records is safe - 35 consecutive holes without a bogey to start a US Open. Since 2012, Day has made all five Open cuts, and has four top-10 finishes. Even with some rain forecast for overnight, look for a tougher test on Saturday, with tucked pins and a longer course. "I'm not saying that this is the week or isn't the week, but I like the way this golf course suits me and we're off to a good start. I guess it's rare you get through a US Open or any major without some kind of a hiccup". He feels healthy now, but he came in rusty - and it showed in his opening round.
"It doesn't affect the game plan one bit, and it doesn't really affect the mindset", he said. Hopefully I've got a lot of the bad stuff out of my system (on Thursday) and some parts (Friday). But I think at the end of the day it's competitive rounds with a card in my hand that I need and I've been very light on them this year.
After Thursday's round, McIlroy and his coach Michael Bannon discussed his swing issues.
"Having a win this year at Honda, being in contention at majors in the past, and having The PLAYERS win has definitely done a lot for me", Fowler said. I couldn't possibly shoot any higher than I did, I just struggled on the greens.
Rickie Fowler did what he had to do to take the lead in the first round of the U.S. Open. He has four major titles, plus a FedEx Cup title last season after winning the Tour Championship.
"It's been the best preparation going into a major", Day told reporters.
Rose was also vulnerable at 2 over, a score that left him one shot outside the cut line with Friday's later starters still to tee off. 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. But it could just as easily be a turning point in the competition this weekend.
"I shot myself in the foot yesterday and gave myself too much to do", he said afterwards.
Another U.S. Open first for Xander Schauffele.