Rickie Fowler was delighted to have kept things simple en route to a stunning 65 that earned him the clubhouse lead on day one of the U.S. Open.

Fowler was the pick of the morning starters at Erin Hills, capitalising on softened greens and a lack of wind early in the day to fire seven birdies in a bogey-free round.

By finishing on seven under, the world number nine matched Tom Weiskopf and Jack Nicklaus' record for the lowest score to par on the opening day of the tournament.

"You don't get many rounds at the U.S. Open that are stress-free," Fowler told reporters.

"I just did a good job, knew I needed to drive it well, and from there [I was] just able to continue to swing well and hit good shots and roll a couple in.

"So, [it was] a simple day when you look back on it, how we kind of pieced our way around the golf course."

Fowler attributed some recent adjustments to his game as the main factor to his success this season and during Thursday's opening round.

"I feel like I'm better throughout my whole game," Fowler said. "I've been able to tighten things up. I used to not be a very good bunker player, and now I feel like I have a lot of confidence, and stats show I'm one of the best.

"That's definitely been something that's been nice to have on days where you're not exactly on and just understanding and freeing yourself up because you know if you might miss something, okay, I'll just get it up-and-down.

"I've been driving it well. Driving stats have gone up. Just hitting the fairways has made it a little easier and that's definitely something that makes a difference out here."

Sergio Garcia's victory in the Masters earlier this year means Fowler is now regarded by many as the best player in the world without a major title to his name. The American is proud of the distinction, but would ultimately like to shed the label.

"I take it as a compliment," he added. "There are a lot of really good players out here that haven't won a major. So it would be nice to get rid of that at some point.

"I'm not saying that this is the week or isn't the week. But I like the way this golf course suits me, and we're off to a good start. There's definitely a lot of golf to be played."