The 21-year-old golfer equaled Tiger Woods' 1997 record winning score of 18 under par to realize his childhood ambitions of donning the green jacket
on Sunday as he swept through the field to become Masters champion at Augusta.
An ice-cool display made him the second-youngest winner -- behind only Woods, who was 155 days younger that year -- and only the fifth man to have led from start to finish over the tournament's four days.
"I miss her a lot, and I wish she could have been here," Spieth told CNN's Don Riddell in the aftermath of his triumph as he opened up about younger sibling Ellie, who was not able to attend the tournament.
"But I can't wait to get back to her and maybe let her try on the jacket.
"I'll have to bring her back a present from here. That's what she'll be expecting."
Amid all the pressure of playing professional golf, Spieth's 14-year-old sister provides him with perspective.
"How has she shaped my upbringing? Well, she's the most special part of our family. She's the funniest part of our family," he said.
"I love having her around. She's an incredible sister, my biggest supporter. She is somebody who you can watch and then reflect on the big picture of life and understand that all these frustrations in a day, or in a round of golf, are really secondary.
"We wouldn't have that realization without her."
At the age of just 14, the prodigy from Texas -- who was named after basketball legend Michael Jordan -- had been clear about what he wanted: his aim was to take the Masters title one day.
And he betrayed virtually no sign of nerves throughout his stunningly dominant performance
, letting slip only a muttered "oh dear" when he marginally sliced a tee shot halfway through the final round.
Last year, Spieth lost the lead just before the nine-hole turn on the last day -- but he never looked like being denied this time, beating Phil Mickelson's Masters record of 26 birdies for good measure.
"To sit with this jacket on and to be a part of the history of Augusta National and the Masters was something I watched slip away last year," said Spieth, who described the reality of winning as "even better" than his dreams.
"I had a chip on my shoulder (about that). I carried some momentum into this week and it all came together, right at the right time."
Shown a picture of himself wearing one of the most coveted pieces of clothing in sport, Spieth, born in Dallas, added: "Putting on the jacket, it looks good. It looks good. I'm OK wearing green!"
He couldn't stop grinning as he said that he hoped to be finishing his final Masters appearance in 50 years' time, but added that he would "still remember what it was like walking up the 18th hole today."
And as he looked less far ahead, he revealed that he would be staying true to his roots at next year's Champions Dinner.
Asked what he would put on the menu for that event, he said: "It would be some form of Texas BBQ."
The unassuming Spieth's success brings to mind other stars whose supreme ability and self-belief saw them become major champions in the early days of their careers.
In 1985, German tennis player Boris Becker stunned Wimbledon when, at the age of 17, he defeated Kevin Curren to become the event's youngest ever men's champion -- a record that still stands today.
Becker said people "thought I had done something I wasn't supposed to do, something that shouldn't have been possible. But I did it -- and then I did it again at 18, just to make the point."
American player Michael Chang was 118 days younger than Becker when he won the French Open in 1989, while Swiss star Martina Hingis was just 16 when she triumphed at the 1997 Australian Open.
Last year, at the age of only 15, Martin Odegaard became Norway's youngest international footballer
when he played in a friendly against the United Arab Emirates, provoking huge media interest and the attention of Europe's top clubs, before he signed for Spanish giant Real Madrid.
For them, as for Spieth, perhaps success was meant to be from the earliest days.
And as he looked at a picture of himself with a golf club in hand, taken at the age of 6 or 7 at his grandparents' home in North Carolina, he reflected on the determination that had put him in the green jacket, referring to another Major winner.
"How about the focus on that swing?" he asked. "That's a little John Daly-like there, isn't it?"