Willett, who pulled out before the start of his second round, was heading towards the Erin Hills exit anyway after an opening round 81.
Justin Thomas eagled 18 to get to 9-under 63, matching the major scoring record and breaking Johnny Miller's U.S. Open record for low round in relation to par.
"Dustin Johnson, Rory McIlroy and Jason Day are all out of the US Open 2017 at Erin Hills". "If you hit it off the tee you can score".
"Obviously, an awesome day, " said Thomas, a Louisville native who played his college golf at Alabama. That was the kind of day it was and the kind of Open it is, as scores are unprecedentedly low and everyone seems fearless.
Westwood had bogeyed the third and fifth before a superb tee shot on the 239-yard sixth - which played as the most hard hole on Thursday - set up a birdie from 18 feet.
He had a chance to extend his lead to two but missed an 11-footer for birdie on 18.
He then drilled a 300-yard second shot to around eight feet before rolling in his eagle putt to roars from the galleries. Seven other players are within five shots of the lead.
However, he left his chip to the green short and then putted through the green and off it with his fourth shot.
"Out here I'm just thinking a lot about my stroke, stance, stuff you would rather not be thinking about, you'd rather think about line of pace". There were certainly some Father's Day gifts purchased in the merchandise tent.
"The greens were still receptive to good shots, but they were firmer and faster", said Fowler.
QUOTABLE: "I just get a little shaky and jittery on putts, and that's what happened on 15".
Neither did McIroy and Day, though all three made their share of trips into the club-grabbing fescue as well.
Reed was one of the biggest movers, powering up the board with a dazzling seven-under-par 65 that included four birdies on the front nine against one bogey. He said he has a plan in the works for Sunday. "On Friday it was the opposite". Kim is three shots back and one ahead of Patrick Reed, Russell Henley and Charley Hoffman.
Anything can change in an Open, such as the career trajectory of fan favorite and first-round leader Rickie Fowler (68), who is only two shots behind.
However, not all Americans fared well.
The 30-year-old Harman has five top-10 finishes and two victories since joining the tour in 2012, most recently at the Wells Fargo Championship in May.
"Uh yeah, I do", Harman said when asked if he still carries that chip on his shoulder this week.
"I've been striking the ball well".
"It's just been trying to figure it out on and around the greens".
"Guess what? We get to go home today because Daddy played poorly", Day said to his son, Dash, before walking over to sign autographs. "So that just kind of gave me a confidence boost, knowing I can hit those shots".
Koepka had the lead until he turned a birdie chance into a bogey on the par-5 first hole after making the turn. The Japanese star birdied six of his first eight holes Friday, finishing round two at five under for the tournament. Fowler lost his lead with three straight bogeys on the back nine.
And Scotland's Martin Laird is putting together a solid tournament with nine birdies and nine bogeys in his opening three rounds.
One thing you can count on for certain on Sunday is that the streak of six majors being won by a first-time victor will grow to seven.