Heading into the final round at Erin Hills in June, the American was one shot off the lead but would eventually fade to finish in a tie for ninth.
At Quail Hollow on Sunday, Thomas made no mistake, conquering the notorious "Green Mile"
with a final round of 68 to win the 99th PGA Championship by two shots.
Chants of "let's go JT!" rang around the spectators at the 18th green before Thomas' proud father emerged from the crowd to hug his son -- golf's newest major champion.
"It was very special," Thomas told CNN Sport, reflecting on their warm embrace. "I'm not too much of an emotional person. I get excited, I get down, but in terms of crying it hasn't really happened to me in the past."
"It was the probably as close I'm going to get sharing that with him."
Like father, like son
Thomas, who took up the game at the age of two, grew up surrounded by golfing mentors
His father Mike has been head professional at Harmony Landing Golf Club in Kentucky since 1990, and his grandfather, Paul, was club pro at Zanesville Country Club in Ohio -- once playing alongside Arnold Palmer in a PGA Tour Champions event.
Thomas remembers attending the 2000 PGA Championship at the Valhalla Golf Club near his hometown of Louisville, Kentucky.
Back then, aged just seven, Thomas watched Tiger Woods secure his fifth major title, and also took home an autograph from Jack Nicklaus.
Seventeen years on, Thomas has now joined golf's elite.
"I've just put so many hours of work in. So much of my life I've dedicated to golf, aspiring to win my first major championship. To be able to do so aged 24 is awesome."
Winning the final major of 2017 caps a memorable season for Thomas who has now won four titles this year. In January, he also became the youngest-ever player to shoot 59 -- en route to victory at the Sony Open in Hawaii.
Thomas' father always keeps the ball as a memento when his son wins a tournament and, at this rate, he's going to have to get a bigger mantelpiece.
"Any time he can put a ball on the rack it's great," Thomas said. "They don't come quite as frequent as they did when I was a junior golfer ... so to add the first major is great.
"(Winning the PGA) almost deserves its own rack, being the first major. It's such a big win, not only for us and my team, but for my career. I'm just so happy we could all share it together."
With more that $7 million prize money banked this season and now ranked sixth in the world
, Thomas is hoping his biggest win to date can launch his career into a new orbit in the years ahead.
"I feel like the sky's the limit," he says. "I can do a lot of great things but none of them will happen if I don't continue to work hard.
"You know, it's in my own hands. I want it badly, I've wanted it badly for a while, and I'm glad to add another stepping stone in my career. Hopefully it's a springboard to even better."