Rory McIlroy hits his tee shot on the first hole during the second round of the 2017 U.S. Open at Erin Hills in Erin, Wis. on Friday, June 16, 2017. (Copyright USGA/John Gress)

Dress rehearsals are all very well but Rory McIlroy confessed that when the curtain went up he was unprepared and fluffed his US Open lines.

The world No 2 followed his nightmarish 78 of Thursday with a one-under par 71 yesterday, concealing another hit-and-miss day with four birdies in his last six holes to miss the cut comfortably on five-over par.

“I think just in practice I was really, really good, and I just wasn’t able to translate that onto the golf course,” said McIlroy, who has played just six events this year and none since The Players four weeks ago.

"I played 54 holes around here before the golf tournament, and I felt really, really comfortable.

"I drove the ball well, my irons were good. Everything was in good shape.

"But you never really know until you put a card in your hand and you're under the gun a little bit.

"Some of the weaknesses and flaws that are in my game at the minute showed up over the last couple of days.

“But I saw some positives on the way in and hopefully I can take them to the Travelers next week."

Shane Lowry confessed after his opening 71 that the weight of expectation weighs heavy in an event like the US Open and he was better yesterday, despite admitting to some mental errors in a 74 that left him eight shots behind the leaders on one-over par.

It’s not just the expectations of those watching around the world but a self-imposed pressure and McIlroy’s disastrous opening round owed as much to his determination to regain his throne as golf’s crown prince as his rustiness.

While he was hitting the ball beautifully down those 60-yard corridors in his practice rounds, they narrowed considerably when he was handed a scorecard.

"Coming off an injury, I was a little anxious going out there (yesterday)," he said of round one, describing his transition as a "lunge".

"I got off to a good start, but it sort of caught up with me as the round went on.

"I think the more rounds I can play, I'm hopefully going to get rid of all that stuff and hopefully strip it down to what you saw the last six holes."

Rory McIlroy during the first round of the 2017 U.S. Open at Erin Hills in Erin, Wis. on Thursday, June 15, 2017. (Copyright USGA/John Gress)

Needing a round of 68 to have a fighting chance of being around for the weekend, McIlroy was far more accurate from the tee yesterday, hitting 11 of 14 fairways compared to just five on Thursday.

His problem was getting the ball in the hole with his new TaylorMade Spider Red putter, but he insisted it was the indian and not the arrow that was to blame as he took 30 putts.

After missing a six-footer for birdie at the 10th, his opening hole, he missed from 15 feet at the 11th, birdied the 13th from 13 feet but then drove into the deep rough and bogeyed the 14th.

A six-footer for birdie slipped by at the 15th and while he saved par from 12 feet at the 16th and nine feet at the 17th, he three-putted from par from just off the 18th and then took four putts from just short of the par-five first, racking up another bogey.

When he thinned his pitch through the back of the second and dropped another shot, he angrily speared his wedge into the turf before turning back to repair the damage.

He made bogey there and dropped another shot at the third to slip to third last on nine over and out of the event before those late birdies at the fourth, fifth, seventh and ninth smartened up the scorecard.

“I started to let it go a little bit on the back nine there today and showed what I can do with birdies at four of the last six,” McIlroy said.

"At least I know it's in there."

Shane Lowry watches his tee shot on the seventh hole  during the first round of the 2017 U.S. Open at Erin Hills in Erin, Wis. on Thursday, June 15, 2017. (Copyright USGA/Jeff Haynes) — Shane Lowry watches his tee shot on the seventh hole during the first round of the 2017 U.S. Open at Erin Hills in Erin, Wis. on Thursday, June 15, 2017. (Copyright USGA/Jeff Haynes)

Lowry's opening 71 might have been a 68 or 69 had he not lost focus towards the end of the day.

And with the USGA tightening up the pin positions and the greens speeding up, he was on the back foot from the off yesterday.

He failed to birdie the first, then drove into sand and short sided himself at the second before dropping another shot after driving into deep rough at the fourth.

He did well to save par at the 232-yard sixth, where he pushed a five-iron into a cavernous greenside bunker.

But after a birdie from 10 feet at the par-five seventh got him back on track, he three-putted the eighth and found an awkward stance in a bunker left of the green at the ninth, failing to get out at the first attempt.

It turned out to be a good bogey four but at two over turning for home, he was blissfully unaware he was sitting on the cut line, admitting later he though it was the top 70 and ties rather than the top 60 who progressed.

It hardly mattered as he birdied the 198-yard 13th from 15 feet but then followed a bogey the par-five 14th after a poor third with a birdie two from four feet at the short 16th.

"I fought well on the back nine," Lowry said. "I got off to a bit of a shaky start and hit a few bogeys. It was a lot tougher with tricky pins, so I am pretty happy.

"I made a bad mental error trying to step on a lob wedge on 14, made birdie on 16, made hard work of the last, but I am here for the weekend."

Lowry is playing well but despite admiring playing partner Jim Furyk’s surgical play en route a level par total, he still plans to use driver at every opportunity.

"I think the winning score is going to be in single digits — maybe seven under — so hopefully I make a few birdies and give myself a chance," he said.

"If I just keep doing what I am doing, I feel like I know where the ball is going. If things don’t go my way this week I know I have got a good summer ahead of me."

While he was generally tidy on the greens, he knows the putter is the key to his fate here.

"I think you need to hole more 20 footers. You’re not going to hit many shots into 10 feet here; you’re going to need to take advantage of the Par 5s and need a couple of putts to go in for you, a few breaks here and there.

"I am one over and I think if I can get her into red figures tomorrow it will be a decent day's work."