American Spieth, seeking a second consecutive victory at Augusta National and a third major title, was five strokes ahead before he imploded with a bogey-bogey start to the back nine followed by a quadruple-bogey 7 at the 12th.
Though he covered the last six holes in one-under, he had effectively handed the Green Jacket to Englishman Danny Willett as he finished three shots back in a tie for second place, leaving the fans and his fellow players in stunned disbelief.
“I was on (hole) 15 and I was absolutely shocked when I saw Jordan go from five (under) to one (under),” Australian Day said after closing with a one-over 73 to share 10th place. “It's tough. It's tough to win major championships.
“So many things and emotions, so many things go through your mind. Sometimes you just don't feel comfortable on certain shots. And unfortunately he hit a bad shot and another bad shot.”
Spieth's worst damaging moments came at the par-three 12th where he hit successive shots into the waters of Rae's Creek in front of the green before finding a back bunker with his fifth en route to a mind-boggling seven.
“Right now it's unfortunate and I'm sure he's killing himself for it,” Day, who clinched his first major victory at last year's PGA Championship, said of a player known for his mental strength.
“But we all do it to ourselves. Hopefully he just learns from it and gets better.
“You go out and lead for seven rounds at Augusta, he's done a fantastic job,” added Day, referring to Spieth's achievement in holding the outright Masters lead for a record seven consecutive rounds until his meltdown on Sunday.
Like Day, England's former world number one Westwood first became aware of Spieth's stunning collapse while he was playing the par-five 15th.
“I saw the leaderboard when I chipped in on 15,” said the 42-year-old. “I hadn't really looked much until that stage.
“There was a massive scoreboard out there and a lot of 'oohs' and 'aahs'. It happens around here. There is a fine line here between success and disaster on this golf course.”
For PGA Tour rookie Smylie Kaufman, who played with Spieth in the final pairing, it “just kind of stunk” to watch his fellow American's collapse.
“I was really cheering for Jordan as a buddy, and it's unfortunate what happened ... just kind of a weird day for both of us,” said Kaufman, who struggled to an 81 to end his first Masters appearance. – Reuters
Original source: Peers shocked by Spieth meltdown