Fowler exploited ideal, overcast conditions for the early starters to fire 10 birdies and two bogeys at Los Angeles Country Club, matching the mark set by Branden Grace in the 2017 Open Championship at Royal Birkdale.
It was also the lowest score ever recorded in a US Open, England’s Tommy Fleetwood making the most recent of the six previous 63s in the final round in 2018.
Yet Fowler amazingly held that distinction on his own for less than 30 minutes as Schauffele, playing two groups behind, carded eight birdies in a bogey-free 62 of his own.
At eight under par the American duo led by two shots from compatriot Wyndham Clark and former US Open champion Dustin Johnson, with Rory McIlroy and Brian Harman on five under.
World number one Scottie Scheffler and Bryson DeChambeau were two strokes further back, while a frustrated Jon Rahm threatened to break a club over his knee as he struggled off the tee, but still managed to post a 69.
Playing alongside McIlroy, US PGA Championship winner Brooks Koepka carded a 71 which was matched by defending champion Matt Fitzpatrick.
Fowler has recorded eight top-five finishes in the majors, including in all four 2014, and was runner-up to Patrick Reed in the 2018 Masters following weekend rounds of 65 and 67 at Augusta National.
The native Californian had failed to qualify for the last two US Opens as a loss of form saw him tumble to 185th in the world rankings, but he came into the week on the back of successive top 10s on the PGA Tour and ranked 45th.
“It’s definitely been long and tough,” Fowler said of his road back to the game’s upper echelons.
“A lot longer being in that situation than you’d ever want. But it makes it so worth it having gone through that and being back where we are now. I would say we’re starting to get maybe as close as we’ve ever been to where I was through 2014, 2015.
“It was a great day out there. The first few days this week I was not feeling very comfortable or making many putts but I kept working on the range and finally a couple of things clicked a bit yesterday (Wednesday).
“Then it was just a case of going out there and trusting it and letting things happen.”
Like Fowler, Schauffele started on the back nine and picked up shots on the 10th, 12th and 14th before storming home in 30, aided by a birdie from 60 feet on the fifth.
“It’s not really what you expect playing a US Open, but monkey see, monkey do,” said the Olympic champion, who has never finished worse than 14th in six previous US Open starts.
“I was just chasing Rickie up the leaderboard. Glad he was just in front of me [But] it’s just Thursday. It’s literally just the first day of a tournament. It’s a good start. You just wait until this place firms up. It’s going to be nasty.
“I’m going to take what the course can give me, and today it gave me a low one, and we’re going to have to assess it as we go on.”
McIlroy raced to the turn in 30 with five birdies in his first eight holes before following a run of six pars with a birdie on the 124-yard 15th, where Matthieu Pavon and Sam Burns both made a hole-in-one.
However, the four-time major winner then dropped his only shot of the day on the 18th and did not speak to waiting reporters after being required to undertake a drug test.