Defending champion Jordan Spieth, left, helps 2016 Masters champion Danny Willett, of England, put on his green jacket following the final round of the Masters golf tournament Sunday, April 10, 2016, in Augusta, Ga.  (AP Photo/Chris Carlson)
Defending champion Jordan Spieth, left, helps 2016 Masters champion Danny Willett, of England, put on his green jacket following the final round of the Masters golf tournament Sunday, April 10, 2016, in Augusta, Ga. (AP Photo/Chris Carlson)

Augusta, Ga. — The walk from the ninth green to the 10th tee at Augusta National is a relatively short one, taking you past the grand old clubhouse on one side and, on the other, the 18th green, where, late in the day on the second Sunday in April, the gallery is already thick with fans and anticipation.

There is just enough time on that walk for a man to think, maybe think big, and to take a peek, maybe a long peek, at the giant leaderboard looming over everything. That short walk, especially if you are leading the Masters, is a journey into your own mind.

Fifty-six other golfers had already made that walk by the time Jordan Spieth got there late Sunday afternoon. At that point, he was in complete command of the Masters for the second year in a row. His lead was five shots — over a 28-year-old Englishman named Danny Willett. Spieth was nine holes from forcing another recalibration of his place in golf history. There had been no one better, one could safely say, at such a young age.

What happened next, though, upended all that we thought we knew about golf, defying belief, even in the context of a tournament that, in 79 previous editions, thought it had seen it all. With the world watching, Spieth, 22, gave away the lead, the tournament and the green jacket with an epic meltdown that will rank among the most horrific of all time, handing the championship to a grateful Willett.

Willett is a Yorkshire native and the 12th-ranked golfer in the world entering the week, and he is both a great golfer and a great story. He teed it up in this tournament this week only because his nine-months-pregnant wife delivered a week early, rather than on their due date — April 10. Sunday. He shot a sterling score of 5-under-par 67 on Sunday, for a 72-hole total of 283, three shots better than fellow Englishman Lee Westwood and Spieth.

But as long as golf is played, they will remember this day, and they will remember it not so much as the day Danny Willett won the Masters but as the day Jordan Spieth blew it.

When Spieth, this tournament’s defending champion, opened his back nine Sunday — where, by tradition and cliché, the Masters is said to officially begin — he went bogey-bogey on 10 and 11. Fine. It was surprising, but he still led by three shots.

Then, on the par-3 12th, arguably the most famous hole in golf, Spieth dunked not one but two balls in the creek fronting the green. By the time he cleaned up the awful mess, he had made a quadruple-bogey 7 — and despite a valiant effort to right himself down the stretch, Spieth could not recover.

He may win several more green jackets to go along with the one he earned here a year ago, and he made win a dozen more major championships to go along with the two he took in 2015. But as long as he sticks his tee in the ground, he may never get over the way he lost this one.

Willett was still on the course, three groups ahead of Spieth, when the latter’s score on 12 went up on the leader board. Playing the 18th hole in the lengthening shadows of early evening, acutely aware of what was going on behind him and what was at stake, Willett finally removed the off-white sweater he had been wearing all day, revealing a lime green shirt. It would later clash with the deeper green of the champion’s jacket, but Willett hardly cared.

Who was this man in blue? One moment Spieth was Tiger Woods, so young, so good, so dominant. He was about to become the first golfer to win back-to-back Masters in wire-to-wire fashion in history. The next minute he was Greg Norman, naked and alone in front of the world, melting down and handing away the Masters.

Such a disastrous stumble has ended the tournaments — if not the careers — of lesser golfers than Spieth. Twenty years ago, Norman, who led by six shots entering the final round, made a similar series of disasters and never managed to stop his freefall, eventually losing by five.

But here, Spieth somehow managed to gather himself by the next hole, the par-5 13th, and went to work. He striped his drive, reached the back of the green in two and made birdie, lifting him to 2 under for the tournament.

He missed a birdie putt at 14 but drilled a six-footer — the sort of midrange knee-knocker he had been draining all week — for birdie at 15. He was now two back. A near-perfect 8-iron into the 16th green left him a delicate eight-footer for another birdie, but this one slid by on the high side. Hoped-for miracles at 17 and 18 failed to materialize.

Concerned by a sudden case of the blocks Saturday — laid most bare by a bogey/double-bogey finish at 17 and 18 when he pushed his drives on each into the trees, causing him to lose three-quarters of what had been a four-shot lead — Spieth flew in his swing coach from Dallas on Sunday morning for an emergency session on the range.

Everything seemed fine for nine holes — more than fine, actually. Spieth made four straight birdies to close out the side, moving to 7 under. But suddenly Spieth, perhaps the most steady, steely golfer of his generation, got sloppy off the tee, much as he had on Saturday. At 10, he failed to get up and down from the right bunker. Bogey.

At 11, he missed a six-foot par putt, the kind he had been draining with uncanny consistency all week. Bogey-bogey.

He moved to the 12th tee, still in the lead, but now by just one thin stroke. He drew his club back, the last moment when everything still made sense.