This level-headed 21-year-old may have a golf game to match his temperament but it is producing some pretty crazy scoring around Augusta National this week, his second-round, six-under-par 66 last night a wonderful companion to his opening 64 on Thursday for last year's rookie runner-up.
It is already enough to earn him a place in the record books, Spieth registering the lowest 36-hole score in 78 Masters tournaments, his 130 completed yesterday a shot better than Raymond Floyd's total in 1976; his cards for the past two days recording 15 birdies and just one bogey.
“I don’t know what course Jordan is playing but it’s not the same one I’m playing. Wow,” an awestruck Darren Clarke said as he completed his second-round 71 that ensured he will at least continue to be in the same field.
Spieth, at 14 under par, stands five strokes clear of his nearest rival, fellow American Charley Hoffman, with a seven-shot cushion between him and the rest of the field, with Dustin Johnson bogeying the last to fall to seven under, albeit with a five-under 67.
Johnson shares third place with English duo Justin Rose and Paul Casey, who shot a 70 and 68 respectively, while Phil Mickelson shot a 68 to move to six under. Rory McIlroy's Masters dream, meanwhile, and the career slam of majors victory here will bring, may have to wait at least another year.
The Irish world number one had begun his round already a dozen shots behind Spieth and will start Saturday's third round still 12 strokes adrift of the leader, his second consecutive one-under 71 taking him to two under for the week, alongside defending champion Bubba Watson, Patrick Reed and Tiger Woods back under 70 at Augusta for the first time since 2011 with a 69.
It was a Jekyll and Hyde round for McIlroy, a monstrous first nine of 40 followed by a delightful 31 on the way home that included some familiar magic from the four-time major winner, not least his 181-yard approach to the par-five 13th to three feet for an eagle.
There was a bogey at 14 but there was no sign of McIlroy giving up the ghost as he might once have done. He birdied the par-five 15th and then chipped in from the edge of the green on 17 to move into red numbers at one under and signed off with another birdie to close.
Much like McIlroy's round, Ireland's other Masters competitors experienced a full range of emotions at Augusta National on Friday.
For Shane Lowry and Padraig Harrington there was disappointment at missing the cut, but for Graeme McDowell and Clarke, the promise of a weekend's play at Augusta National brought only positives. Clarke, the 2011 Open champion, will be hanging around after his 71 sent him into Saturday's third round at one over par.
Europe's 2016 Ryder Cup captain shares the same score as McDowell, who carded a four-birdie, six-bogey 74 for his second round.
Today's third round will see McDowell at Augusta National on a Saturday for the first time since 2012 and the good news for the former US Open champion is that when he has made the cut, just twice in seven previous attempts, he has finished inside the top 20.
“It’s nice to be here for the weekend, get another couple of rounds under my belt and keep building for the rest of the season. Of course I’d love a big finish, but I need rounds, I need reps, I need to see shots.”
After a trying first round, debutant Lowry improved on his opening 75 with a level-par 72 featuring two birdies and two bogeys last night that left him with a nervous wait at three over par, the Offalyman remaining optimistic that an incoming storm and gathering winds would push the survival mark up and make life difficult for those still on the course.
Alas it was not to be for the world number 46, who found himself one shot adrift, those on two over the ones to survive. Harrington, though, knew his fate after following an opening even-par 72 with a five-over 77.
The three-time major winner, back in the PGA Tour winner's enclosure last month at the Honda Classic, had seen a promising first round get away from him with back-to-back bogeys at 16 and 17 on Thursday. “It was a disappointing finish yesterday evening and I sort of carried that into today,” Harrington said. “It was one of those days when nothing was really going for me.”
The polar opposite applied to Spieth, whose five-shot margin equals the largest 36-hole lead, previously enjoyed by Herman Keiser in 1946, Jack Nicklaus in 1975 and Floyd in '76. All three of his predecessors in that position went on to win the Masters but as far as Spieth is concerned, history will be meaningless if he is unable to join that victorious trio in pulling on a Green Jacket on Sunday night.
“I was just excited to be off to a great start, having a chance to control my destiny in this golf tournament,” Spieth said, before adding: “As far as history and what happened the last couple days, doesn't mean anything, unless I can close it out. I don't want to go in as the 36 hole best record, but somebody who didn't win. “So, ultimately, I just need to set a goal for myself, continue to strike the ball the way we have been playing and try and shoot under par rounds on this weekend.”
A 21-year-old running away with the Masters is a familiar plotline for all those who remember Tiger Woods winning his first Green Jacket in 1997 with a record low score of 270 and by a record margin of 12 strokes.
Woods, now 39 and rebooting his game after a nine-week emergency sabbatical, was asked what it was like to be on the other end of a runaway lead, an impressed Woods said: “Well, the difference is that he's separated himself between first and third. I didn't have that separation after two rounds. I believe I only had a three-shot lead at the time. So there's a big difference. He's put out a big enough gap between the rest of the pack.”
Now it is Spieth's turn to chase Tiger's milestones over a Masters weekend, Woods having shot a 65 and 69 to close out the first of his 14 major championships. There's still 36 holes to go and stranger things have happened but in the majors but Spieth does not look like a man ready to come back to the field just yet.