As he did at Chambers Bay, Johnson carded an opening 65 to claim the lead, with Spieth this time a shot closer thanks to a five-under 67 which made a mockery of concerns about a lack of preparation in his bid for a third straight major.
With the course initially defenceless before the wind strengthened, 1999 champion Paul Lawrie, England’s Danny Willett, Jason Day, Retief Goosen, Zach Johnson and Robert Streb all shot 66, with US Open runner-up and 2010 Open champion Louis Oosthuizen among those to match Spieth’s score.
Sweden’s David Lingmerth even raised hopes of the first 62 in major history with a record-equalling front nine of 29, but Tiger Woods duffed his approach to the first into the Swilcan Burn and limped to a 76, his worst score as a professional in the Open at St Andrews.
However, attention was rightly focused on match 17, with Spieth chasing the third leg of an unprecedented calendar grand slam and Johnson trying to claim a first major title after his latest near-miss.
Somewhat mischievously paired together by the R&A, the American duo matched each other almost shot for shot in covering the front nine in 31 and reaching six under after 12.
Spieth proved he is human after all with bogeys on the 13th and 17th – where he found the famous Road Hole bunker – before holing a curling birdie putt from 20 feet on the last.
“I’m very pleased with the start,” said the 21-year-old, who is aiming to match Woods and Ben Hogan in winning three majors in a season. “I saw a 65 in our group and if DJ keeps driving it the way he is, then I’m going to have to play my best golf to have a chance.
“It’s hard to argue with somebody who’s splitting bunkers at about 380 yards and just two-putting for birdie on five or six of the holes. I don’t have that in the bag, but I’ve played enough golf with him to where I believe in my skill set that I can still trump that crazy ability that he has.
“I expect when he stands on the tee it’s going to be up there miles and down the fairway. I also expect that I can birdie each hole when I stand on the tee. It just happens to be a little different route.”
Spieth and Johnson took the same route to the green on the 72nd hole at Chambers Bay, but while Spieth made birdie, Johnson three-putted from 12 feet to finish a shot behind.
“I think he played extremely well at Chambers. It’s not like he really messed up,” Spieth said. “It just was an unfortunate last hole for him. I certainly expect him to be a guy to beat every single time you play. He’s got as much talent or more than anybody. You just have to outplay him.”
Spieth’s decision to compete in the John Deere Classic last week and only arrive in St Andrews on Monday had been questioned, but the world number two had no such qualms.
“I wanted to come off a competitive tournament,” said Spieth, who won the tournament for the second time in three years. “I could have played the Scottish Open but I wanted to go somewhere I was comfortable playing and figured I could get in contention and feel the nerves, and that’s what happened.
“Our game plan worked out perfectly and Michael (Greller, his caddie) has walked two or three extra rounds already. He also was out here at 4:00 something this morning walking the course and the pins. It takes a little extra work but, all in all, we had full and complete trust in our knowledge.”
Johnson insisted on Monday there were no mental scars after Chambers Bay and set out to prove his point with an eagle from six feet on the fifth and five birdies in a flawless round.
“Nothing bad happened at Chambers Bay, so I wasn’t disappointed, really,” the 31-year-old said. “I did everything I was supposed to. I couldn’t control what the ball was doing on the greens there.
“There’s really no bad feelings from that, only good. I played really well and then it carried over to today. Any time you shoot 65 it is very pleasing. I thought I played well today, I made two key par putts on 16 and 17.”