The Texan carded a career first quadruple bogey to hand Willett a three shot lead
Danny Willett has won the Masters at Augusta, his first major title and becomes the first win by an Englishman in 20 years.
The 28-year-old shot a closing 67 for a 5-under 283 total with defending champion Jordan Spieth tied for second.
Willett, a four-times winner on the European Tour competing in his second Masters, birdied three of the last six holes to cap off a bogey-free display and become only the second Englishman to win the coveted Green Jacket and $1.8m top prize, following three-times champion Nick Faldo.
Spieth entered the day as the outright leader on three under par, one shot clear of compatriot, Smylie Kaufman.
The Texan began brightly, a birdie on the second was only undone by his bogey on the fifth that inspired a run that saw him pick up four consecutive shots to round off his front nine.
At this stage, the 22-year-old was seven-under-par and the back nine appeared it would be nothing more than a procession.
Jordan Spieth inconsolable on the 18th before closing out his round. Image: Chris Carlson / AP/Press Association Images
Instead, Spieth picked up bogeys on the 10th and 11th, before carding a career first quadruple bogey on the 12th.
"It's tough, really tough" he told CBS.
"Four birdies in a row and I knew that even par (on the back nine) is good by at least a shot and sometimes that makes it hard. You go away from the game plan and start playing conservative. A few weak swings and suddenly I am not leading any more."
Willett, meanwhile, kept the pressure on the Spieth carding a bogey free 67 for his final round and finished 2 shots clear the American and Lee Westwood.
Willett had been in doubt for the year's first major before his wife Nicole gave birth to the couple's first child.
Her due date had been Sunday but the baby, named Zachariah James, was instead born by C-section a week ahead of the tournament.
After his win, he said: "You can't really describe your emotions and feelings. Someone has got to win and today was my day.
"I played great golf. It has been a fantastic week. It was just a very surreal day... and a crazy, crazy week."
The Sheffield man, who is the son of a vicar, left school at 16 and quit a local college course after a month, declaring that he "hated it". He then made the move to the US, attending Jacksonville State in Alabama for two years.