Five players, including Thomas, controlled their own playoff destiny if they could capture the Tour Championship this week.
Canada's Corey Conners has earned his PGA Tour card. Thomas, who finished at 11 under, had a putt on No. 18 that would have eventually gotten him into a playoff with Schauffele that narrowly fell to the low side.
The competition is the PGA Tour's season-long points race. "He has that belief now that he can make it happen", Spieth said of Thomas.
While, of course, Xander Schauffele won the Tour Championship.
Sergio Garcia has four birdies on a bogey-free round so far.
Justin Thomas is the FedEx Cup champion, a surprise to no one who saw him power his way to scoring records, his first major at the PGA Championship and more PGA Tour victories than anyone this season. While Thomas fell short on Sunday, he still left as the FedEx Cup champion.
Thomas was battling comers from all sides on Sunday, too.
He had $10 million and a shiny new trophy.
Compatriot Marc Leishman also struggled, shooting a 72 to share 24th at three over after entering the Tour Championship as a top five seed.
"It's a really weird day", Thomas told Dan Hicks of NBC.
"I thought it missed, that's why I couldn't even react to celebrate because I thought I just missed a two-footer to win", the rookie said of his final stroke of the season.
Johnny Miller, a two-time major victor who was in the broadcast booth Sunday for NBC, said Saturday that he loved Thomas's swing, which is as unique as a fingerprint. "It was probably the worst putting event that I had this entire year", Spieth said after the final round. He bogeyed the 17th hole to shoot 71 and heads into next week's Web.com Tour Championship at 26th on the Finals list. "I'm sure people were kind of shocked at my reactions or my tone because I was - I mean, I wasn't mad - but my competitive nature, I mean, I was upset. I was glad that it paid off".
His best finish this season came at the Bahamas Great Exuma Classic where he came fifth. He finished in the top five in both of those categories this week.
"The bonus that comes with the FedEx is nice and all, but a major championship cements you in the history of the game", said the 24-year-old Spieth, who has amassed almost $35 million in his short career.
Given a fresh start, the 32-year-old self-taught player quickly capitalized.
He also fancied the prospect of being in the final two groups of a major on Sunday.
The four major championships are bigger, and always will be.
U.S. Open victor Brooks Koepka shot 69 and was alone in sixth place at 272.
However, it would be hard to argue against Thomas capping a career year with those rewards. Now he has the cash to prove it.
"It was a great season, if I could repeat it every year for the rest of my career I certainly would", Spieth said "I knew after the 10th hole that I could win the FedEx Cup and they just didn't quite go my way".
"After the Presidents Cup I get a couple days off and reset the goals and then my dad, Jimmy (his caddie) and myself will go off to Malaysia again".