Defending champion Dustin Johnson, world No. 2 Rory McIlroy and third-ranked Jason Day all made early exits as Americans Brian Harman and Brooks Koepka and Englishmen Paul Casey and Tommy Fleetwood led the field at halfway in Wisconsin.
The quartet largely avoided the deep fescue and took advantage of rain-softened greens to push the leading score to seven under as golf's top trio fell the wrong side of the cut, which came at one over.
Johnson, who defied controversy to win his maiden major at Oakmont 12 months ago, was teetering on the cut mark all the way through his second round late Friday.
But he faltered in the closing stages and rounds of 75, 73 for four over gave the 32-year-old extra time to be with fiancée Paulina and second child River Jones, who was born Monday.
McIlroy, who has missed the last five weeks because of a rib injury, said in the build-up if players couldn't hit the wide Erin Hills fairways they should "pack their bags and go home."
Well, McIroy was forced to practice what he preached.
The Northern Irishman hit only 36% of fairways in a six-over round of 78 on day one, and a second-round 71, despite four birdies in his last six holes, could not save him.
"I showed up for the last six holes, anyway," said McIlroy.
Australian Day limped out with a total of 10 over after rounds of 79 and 75 as he struggles to regain the form that took him to world No. in 2015.
"It's pretty frustrating," he said. "If you hit the fairways the scores are out there."
In all, eight of the top 12 players in the world missed the cut, including Masters runner-up Justin Rose, who shot 72, 74 for two over, Open champion Henrik Stenson and former Masters winner Adam Scott, who both finished three over, and two-time Masters champion Bubba Watson (+4).
But the battle for top spot set up an absorbing weekend.
Unusually for a US Open, which traditionally favors a winning score around par, there were 42 players under par and within six shots of the lead, out of 68 who qualified for the weekend.
Masters champion Sergio Garcia, in a tie for 19th at three under, was the highest-placed player on the leaderboard with a major to his name.
Resurgent Englishman Casey, a former world No. 3, added a 71 to his opening 66 despite a triple-bogey eight on the 14th.
"It's not every day you enjoy a round of golf with an eight on the card, but I'm a pretty happy man," said the 39-year-old, whose best major finish was tied third in the 2002 British Open.
Casey was joined by up-and-coming countryman Fleetwood (70), the world No. 33, left-hander Harman (70), the world No. 50, and PGA Tour winner Koepka (70), ranked 22.
First-round leader Rickie Fowler was one shot adrift after a faltering one-over 73. The American went 28 holes without a bogey and then made three in a row before steadying the ship coming home to stay in contention.
Alongside Fowler were fellow Americans Jamie Lovemark and JB Holmes, while in a group on five under was Japan's Hideki Matsuyama, the world No. 4.
Matsuyama was seven under for the day through 13 and on course to break the major championship record round of 63 but he could only manage five pars to finish for a 65.
American Chez Reavie also shot 65 to climb to four under.
Jordan Spieth, the Masters and US Open champion in 2015, was still alive heading into Saturday on level par.
The best US Open comeback to win after 36 holes was the 11 shots Lou Graham clawed back to clinch the title at Medinah in 1975.
The 117th US Open is wide open.