Adam Hadwin registered five birdies in six holes to help him take the lead at the US Open in Boston ©Getty Images

A superb run of birdies helped Canada's Adam Hadwin take a slender lead on the opening day of the US Open in Boston.

After dropping a shot on the third hole, Hadwin then rattled in birdies in five of the next six to forge ahead at The Country Club in Brookline.

Hadwin cancelled out a bogey with another birdie in the back nine as he finished the first round with a four-under 66.

The Canadian is just one shot ahead of a group of five golfers including four-time major winner Rory McIlroy of Northern Ireland.

McIlroy, seeking his first major title since 2014, led the way courtesy of back-to-back birdies only to post a bogey on the final hole.

The Irishman is joined on three-under by England's Callum Tarren, Sweden's David Lingmerth, Joel Dahmen of the United States and MJ Daffue of South Africa.

Despite holding the narrowest of leads, Hadwin - whose best career finish at a major is tied 24th at the Masters in 2018 - said he felt "surprisingly pretty comfortable".

"I was at ease which was a nice feeling at a US Open and doesn't happen very often," said Hadwin.

"I had a nice little run there at the end of my front nine and knew there were a lot of good strong holes coming in so just kind of kept plugging away.

"I've done such a good job of that over the last month or two, just really having no expectations, taking every shot for what it is, trying to do my best on that individual shot and then moving on.

"I can certainly get ahead of them [shots] like a lot of guys do, especially at a big event like this.

"It's a little bit easy to get your mind racing once you see your name at the top of the leaderboard, but I did a great job of focusing on each individual shot and taking what it was and just trying to do my best on every shot."

There are seven players just two shots behind Hadwin heading into the second round.

Among those includes American Dustin Johnson who was among the stars to cause controversy by joining the Saudi-backed LIV Golf Invitational Series.

Johnson scored a two-under 68 along with compatriots Hayden Buckley, Matthew NeSmith, Brian Harman and Aaron Wise as well as English duo Matt Fitzpatrick and Justin Rose.

Competition is due to continue tomorrow.