Jon Rahm is the defending U.S. Open champion, one shot out of the lead. He will be playing on the weekend at The Country Club with Hayden Buckley, who studied while playing at Missouri because he figured he'd need to find a job after college.
The dozen players separated by two shots going into the weekend include the top three players in the world ranking and four of the top seven: Masters champion Scottie Scheffler, Rahm, Rory McIlroy and Morikawa.
"I think it's great for the game of golf that the highest-ranked players and the best players are up there, especially in the tournament where truly the best player ends up winning," Rahm said.
It also includes two PGA Tour rookies and two players who have never won on tour.
Morikawa was searching for something in his game and found a "baby draw" instead of his traditional fade, and it has been working beautifully at Brookline. He matched the low score of the championship Friday with a 4-under 66 for a share of the lead with Dahmen, the cancer survivor and popular everyman in golf.
Rahm did his best to keep pace with an eagle and a series of big par putts that felt just as valuable. Rahm had a 67 and was in the group of five players one shot behind. That included McIlroy, coming of a win at the Canadian Open, who hit his stride on the back nine with three birdies over his last four holes for a 69.
Not to be overlooked was Scheffler, the No. 1 player in the world, who chipped in from thick rough short of the par-5 14th green for an eagle that brought the Texan back into the mix with a 67. He was two shots behind.
Morikawa, Rahm and Scheffler have combined to win four of the past nine majors. And then there's McIlroy, who has four majors by himself, but none since 2014.
"It's the U.S. Open. No one has taken it deep so far and kind of run away," Morikawa said. "The last few days is a huge confidence booster for me heading into this weekend, and hopefully we can kind of make some separation somehow."
The idea of the U.S. Open is to identify the best players. Some of them require some introductions to major championship contention on the weekend.
Start with Dahmen, who will never be accused of taking himself too seriously, even if he takes his game seriously. He thought about withdrawing from the 36-hole qualifier twice last week, before it started and after the first round.
But he stuck it out, and with a 68 on Friday, plays in the final group of a major for the first time. He joined Morikawa at 5-under 135.
"We don't tee off until 3:45 tomorrow. I typically have to be home at 5 for dinner," Dahmen said. "So this will be different, for sure."
The group one shot behind includes Buckley, who wasn't in the U.S. Open until making a 20-foot birdie putt in a playoff for the last spot in his qualifier 11 days ago.
He was fading, like so many others, with three bogeys during a five-hole stretch around the turn when he got back on track. Birdies on the last two holes gave him another 68.
Also at 136 were Aaron Wise, with one PGA Tour victory and nothing better than a tie for 17th in his nine previous majors; and Beau Hossler, who featured on the weekend at Olympic Club as a teenage amateur in 2012 but hasn't been heard of since then in the majors.
They were examples that the U.S. Open being open to all doesn't just stop with qualifying for the right to play the toughest test in golf.
The Associated Press contributed to this report.