Rory McIlroy benefited from playing in a relaxed manner as he began the U.S. Open with a strong three-under 67.

The former world number one has not won a major since 2014, with his recent struggles often coming in the early rounds, but that was not the case on Thursday.

An impressive showing at the usually tricky Winged Foot took McIlroy to within two strokes of clubhouse leader Justin Thomas by mid-afternoon on day one, with Patrick Reed second on four under.

Four-time major champion McIlroy acknowledged he had taken a different approach this week and it was paying off.

"It's just golf," he said. "But maybe I've been putting myself under too much pressure to get off to a good start. In the first round of a major, you're always anxious to play well. Maybe I've overthought it at times.

"I just went out today, took what was given to me, a little more relaxed, and played really nicely."

McIlroy added: "I think at a U.S. Open, if you can get off to a good start, you're not chasing as much. If you chase on U.S. Open golf courses, that's when you can start to make mistakes and compound your errors a little bit.

"To have that cushion, to be a little more relaxed about your play, not to take on too much, be able to still play conservative golf... I think that's important here."

McIlroy finished with four birdies and just a single bogey but still felt he might have performed even better.

"I three-putted for par on six. There was a couple of other chances I let slip by," he said. "There were chances there to sneak another two or three out of the round.

"But at the same time, 67 here is always going to be a good score."

Indeed, he bristled at the suggestion low scores from the leading players meant the often high-scoring course was now "scoreable".

"JT shot five, Patrick four, myself three, but then after that, if you shoot even par, you're just outside the top 10," McIlroy said.

"I wouldn't call it scoreable by any stretch of the imagination.

"A couple of guys have gone a bit lower than expected, but it's not as if the rest of the field are finding it that easy."