Morikawa backed up his opening round total of 69 with the joint lowest score of the week with a four-under 66 at The Country Club in Brookline.

The 25-year-old is looking to add the US Open crown to the PGA Championship and The Open Championship titles he won in 2020 and 2021 respectively.

He is level on five under with Dahmen who climbed to the top thanks to scores of 67 and 68.

Dahmen scored four birdies, three of those coming on the front nine, and two bogeys to put him in contention for his first major title.

Morikawa’s opening-hole birdie was cancelled out by a bogey on the fourth before he rattled in birdies on the eighth, 12th, 14th and 17th.

"I think what it proves is just you can play this game with many shots," said Morikawa.

"I remember the first time I played with Tiger [Woods], and he hit every shot that called for it. 

"Pin is on the right; you hit a little cut. Pin is on the left; you hit a little draw.

"This is just going to hopefully make my iron play and make my game a little bit more well-rounded rather than just hitting a cut.

"But this week we're just going to work with what we have, and right now it's a little baby draw."

Morikawa and Dahmen are one shot ahead of a group of five golfers including reigning champion Jon Rahm of Spain and another former winner in Rory McIlroy of Northern Ireland.

Rahm and McIlroy scored 67 and 69 respectively to remain in the hunt for another major title.

They are tied on four under with three Americans in Hayden Buckley, Aaron Wise and Beau Hossler.

A further five Americans are level on three under as Nick Hardy, Scottie Scheffler, Matthew NeSmith, Patrick Rodger and Brian Harman battle it out.

Canada’s Adam Hadwin, who led after scoring a first-round 66, slipped to two under alongside Sam Burns of the US and England’s Matt Fitzpatrick.

American Phil Mickelson, a six-time US Open runner-up who was among the stars to cause controversy by joining the Saudi-backed LIV Golf Invitational Series, was one of the big names to miss the cut.