It marked the first time since the world rankings were created in 1986 that the top three ranked players in the world missed the cut at a U.S. Open.
Thomas fired nine birdies and an eagle on the 18th to card a nine-under-par 63 and take over the clubhouse lead on 11 under par, two shots clear of compatriots Brian Harman and Brendan Steele and England's Tommy Fleetwood.
Casey chopped his way to a triple bogey, only to respond with five straight birdies that carried him to a 1-under 71 and make him the first to post at 7-under 137.
The world number two, who earlier in the week suggested players unable to find the fairways should "pack their bags", is now contemplating an early exit following a second-round 71.
The final pairing of Casey and Harman are scheduled to tee off at 2:29 p.m. (1925 GMT), but a forecast calling for the possibility of thunderstorms could disrupt third-round action.
"I made two bad swings on the front nine", Koepka said. He missed almost two months at the start of the year when he was diagnosed with a slight rib fracture, and then the latest break after The Players Championship.
Matsuyama and Reavie each shot a 7-under 65 in the second round of the U.S. Open.
"I really like this golf course; it sets up really well for me, especially if I'm driving it like I did today, " said Johnson, who shot 73 along with a first-round 75 to finish at 148.
ERIN, Wis. (AP) - An 11-year-old golf course shaped from Wisconsin pastureland was sure to bring something different to the U.S. Open.
Zidane pleads with Ronaldo after shock
The Portuguese superstar has won consecutive Champions Leagues at Real Madrid and is now in a side that could win three in a row. In addition to Zizou, Sergio Ramos had also called Ronaldo in a bid to keep him at Real Madrid .
The 28-year-old started day two with a one-shot cushion but a one-over-par 73 opened the door for a four-way tie at the top. I got out of position, but it's the attitude, it's the grit that matters at the end of the week. "Someone has a very good chance of ending up with their first major tomorrow".
Then came the par five 14 hole. "I couldn't possibly shoot any higher than I did".
Dustin Johnson of the United States walks across the 18th hole during the second round of the 2017 U.S. Open at Erin Hills on June 16, 2017 in Hartford, Wisconsin. The last time Day missed a cut in a major was the 2012 PGA Championship, just a month after his son was born.
"I had been swinging it well and it felt really, really good a couple holes later to be picking the ball out of the hole for a birdie". But then he three-putted from long range on the 13th and the 14th, and lost all hope when he missed the green on the 17th while going after the flag.
"I knew going into the day with the rain we had last night and seeing that the course was going to play probably similar to what we saw Thursday morning when I went out, and if you played well and executed, that birdies were out there", Fowler said.
"Yeah, 12 under, I'd have about a 10-shot lead in most Opens", he said.
McIlroy was never in the short grass from the 11th hole to the end on Thursday when he opened with a career-worst 78, and he didn't do almost enough in the second round until it was far too late.
"I was sticking to the same game plan, I was doing the same things", Hadwin said. It's there that the mistake was made: Hadwin tried to play too flawless of a third shot up toward the raised putting surface.