Johnson, who had struggled to a three-over-par 75 in the first round, carded three birdies and four bogeys in a one-over-par 73.

The American is seven shots behind leaders Paul Casey, Brian Harman, Tommy Fleetwood and Brooks Koepka in Wisconsin.

Casey was the only golfer who went in the morning. "But I'm a pretty happy man".

Casey birdied five holes in a row after the rough stretch and was the first player in the clubhouse at seven-under.

Casey overcame a triple-bogey eight at the par-five 14th, his fifth hole, to lift himself into championship contention.

Chez Reavie had an incredible round of 65, but he was not the only person to shoot that score with Hideki Matsuyama showing his class and the world number four is just two shots back now - the Japanese player was tipped by the GM tipster before the tournament. "Even just trying to take my medicine was very, very hard. It was a good eight in the end".

While Erin Hills was still not playing as hard as many past U.S. Open courses, it was beginning to firm up from the early week rain, plus the USGA had a few tricks up its sleeve.

"The greens were still receptive to good shots, but they were firmer and faster", said Fowler. "Part of that is just age and part I'll give credit to Johnny McLaren (his caddie), credit to my wife and my little boy".

Matsuyama, at number four the highest ranked player still in the field, starts at five-under along with young South Korean Kim Si-woo, amateur Cameron Champ, PGA Tour rookie Xander Schauffele and veteran Brandt Snedeker.

He recovered to drain a 13-foot birdie putt on the par-three 13th, but thereafter was unable to build any momentum over the remainder of the opening nine holes.

And then, the old McIlroy kicked into gear and finished with a flurry of gained shots as he kept the ball in play off the tee and proved majestic with his mid-irons to set up several birdie chances.

"Even though it's very disappointing to not be here on the weekend, I think these last two rounds will serve me well going into the summer", McIlroy said.

Most freakish about this day was that as many amateurs broke par as top 10 players in the world - two apiece. Johnson (+4) can't be too upset to be travelling home to California to see his newborn baby. "But you don't really know until you put a card in your hand and you're under the gun a little bit", said McIlroy, who said goodbye at 5 over.

Under clear skies and warm sunshine, the Erin Hills course still offered plenty of encouragement after a day of record low-scoring on Thursday.

"You'd definitely take it, said Fleetwood, whose previous best finish at the US Open is tied for 27th".

"The worst thing I can do is go and force it, because that's not my game". He twice has been sidelined this year due to a rib injury, and he had played just the Players Championship since the Masters.

Day was particularly disappointed as he felt he had prepared properly for the championship.

"This has been the best preparation going into a major in my career, but the execution was not there", Day said.

One shot back. Jamie Lovemark.

"We're in a good spot", Fowler said. "As of right now, I'm one shot back ... but just more so for the confidence going into tomorrow".

While the former took a share of the haflway lead with a 71 which owed so much to heart and perseverance, the latter submitted to the cut in a performance which is beginning to sum up his miserable season.