Rory McIlroy blames 'tentative' putting for poor opening score at U.S. Open

McIlroy shot a two-over 72 in the opening round of the second golf major of the year, notching two birdies and four bogeys to finish seven shots behind early pace-setters Dustin Johnson and Henrik Stenson.

While McIlroy conceded the patchy greens at Chambers Bay Golf Club were not the best, he insisted that was not the only factor to his inability to produce birdies, after missing the cut at his past two tournaments - the Irish Open and the BMW PGA Championship.

"They are not the best I have putted on but I should be used to it as the last two tournaments I've played have been just as bad," McIlroy told Sky Sports.

"I felt like I played well tee to green and gave myself a lot of looks but did not take advantage of the good shots I was hitting. There were a couple of misreads and a couple of bad strokes in there as well.

"It's hard to pick the line and trust it and then you start making tentative strokes and you are not getting a true roll on the ball. I need to work on that before tomorrow's round and see if I can figure something out."

McIlroy started on the back nine in University Place, picking up a birdie on the 10th hole but then notching bogey, bogey, birdie from the 14th.

Bogeys on the seventh and ninth holes to complete his round left the Northern Irishman with a grimace on his face.