Jason Day is no longer the nearly man of the majors and Rory McIlroy is no longer the world number one – they are the headline stories after the final day of a vintage major championship year.
In truth, Spieth didn't bring his best game to Whistling Straits and yet doggedly pursued and tested the Australian.
Day’s nerve under pressure had been questioned over the last four years – a period during which he finished in the top four in the majors on six occasions without winning. That was up until yesterday’s dominant performance here as he wiped away his frustration to win with the lowest total against par in the history of majors at 20-under – good enough for a three-stroke victory over Speith.
Day laid down a marker early on – building on a two-shot overnight lead by making birdie at four of the first seven holes.
Speith didn’t get close enough after that to apply pressure, and Day finished with a tap-in par at 18 in a flood of tears and relief at finally winning after many reversals of fortunes at this level of the game.
"The biggest thing that prepares you for something like this is just the sheer experience of failure," Day said.
"Knowing you can learn from anything ... that's what gets you mentally tough."
The consolation for runner-up Spieth was absolutely huge as he finished the major season with a record of two wins, a fourth place at the Open in St Andrews and a runner-up finish here.
His total of 54-under for the four majors is one shot better than Tiger Woods managed in his finest year of three championship wins in 2000.
In claiming the runner-up on his own here, Speith is now the new world number one.
Spieth said: “This is as easy a loss as I've ever had because I felt that I not only couldn't do much about it, as the round went on, I also accomplished one of my life-long goals in the sport of golf.
"That will never be taken away from me now. I'll always be a number one player in the world.”
A final round of 69 left Rory McIlroy - after his long injury lay-off - in 17th place on nine-under. McIlroy was one of the first to tweet congratulations to both the champion and the man that has taken over from him at the top of the world rankings.
Golf is Tiger-less at the moment but it has rarely been more fascinating. We may well be witnessing the beginning of a new era led by a generation that Tiger inspired and we possibly also have a new big three in golf in Day, McIlroy and Spieth. Between them they have won five of the last six majors.