Rory McIlroy struggles to build on his brilliant first round at US Open 

If Thursday saw the best of Rory McIlroy, then his second round of the Los Angeles Country Club was marked by the familiar sighs and groans of waning momentum.

At press time, that translated into a score of six under par over 15 holes, which was only one better off than where he started.

No round in the red can ever be considered a bad thing, but at a US Open hitherto unusual in its chances to score, McIlroy regularly wore the look of a man selling himself short.

This was best demonstrated by hitting the floor with an iron on the fourth tee, en route to what would become one of four bogeys. He only carded one in his entire opening of 65, but he was much looser here, albeit with enough quality to redress the balance with five birdies, ensuring he still has a big part to play in this tournament .

How good he will be this weekend will of course be determined by his final numbers, and indeed by the success of the later starters, including overnight leaders Rickie Fowler and Xander Schauffele.

The 34-year-old has so far struggled to build on his brilliant first round run on Thursday

They ripped apart the North Course on Thursday with matching 62s that tied for the lowest round ever at a major, but as of Friday the course has been tickled into a stiffer challenge.

That was reflected in pins in tighter spots and an extra 200 yards in length, which translated into lower scores with the early starters.

Still, it remains a course much friendlier than many we see on the US Open roster. Brilliant and nuanced, yes, but less snappy, especially in the cloudy conditions of the first two days. The potential for birdies was initially shown by Wyndham Clark who improved by three to bring the clubhouse lead to nine. Harris English also had room to improve himself by four to seven.

With those gains possible, it’s fair to say McIlroy didn’t quite get enough. His driving style was generally solid, but his approach game was noticeably declining. After legally hitting 16 of 18 greens on Thursday, he only managed 10 of the 15 he had played here. If he wants to cross the line for a first major in nine years, that’s clearly the area that needs the most improvement over the weekend.

From the 10th he opened with a par, but on the next, a par three of 276 yards, he found the thick greenside rough and could only chip to 4.5 yards. He missed the putt coming back to drop a shot, before picking it up again with a 32-footer on 12.

The turbulence continued with a second bogey after he yanked his drive left on 13, which was typical of his game. Nothing was very out of line, but all facets were just a little less clean compared to his first round.

He stabilized with three straight pars, including a missed opportunity for a 3-yard birdie on 15, before losing a stroke on the 17th when he flew through the green on his approach.

A birdie on the par-five helped first, and another mid-range putt emptied on the third, sending the Northern Irishman down to five under.

His speed picked up, but then the 2011 champion threw an iron into the barranca guarding the front of the green on the 200-yard fourth. His fury was evident and a bogey ensued, before clearing birdies on five and six followed.

It was also a slow-burning day for Matt Fitzpatrick, albeit with the notable rise of an ace on the 115-yard 15th

While McIlroy posted small losses and gains, more dramatic fortune swings affected Dustin Johnson.

He had started his round tied for third at six under, but suffered a quadruple bogey in second. By the 17th hole he had recovered to five under.

It was also a slow-burning day for Matt Fitzpatrick, albeit with the notable rise of an ace on the 115-yard 15th. The defending champion was one over with three to play.

Meanwhile, The Open organizers have confirmed Tiger Woods will not play in Hoylake next month as he recovers from surgery in April.