McIlroy, clearly feeling the pressure was one over at the turn but drove his tenth tee shot almost out of bounds and took a seven to go four over par for his round. He later three-putted the 12th to fall completely out of contention.
His final round was reminiscent of the collapse at the British Open last year when he shot a second round 80
Afterwards he said "It is one of those things I am very disappointed but I will have plenty more chances ... hopefully it will build a little bit of character in me."
"I will reflect on this for the next few days. I lost a lot of confidence in my putting and began second guessing myself," he said.
McIlroy never looked comfortable during his final round after bogeying the first hole and soon found himself in a dog fight as Adam Scott, Tiger Woods and McIlroy's playing partner Angel Cabrera all shot under par with Woods powering through a 32 for the first nine and joining the leaders on the 15th.
McIlroy, who had played nerves free all week found the immense pressure telling on him and it finally came apart on the 10th when his drive ended up a hundred yards off the fairway and he later hit a tree as he tried to extricate himself.
It was heartbreak for the young 21-year-old Northern Irish player who had led through the first three rounds and looked certain to continue on to victory with a four shot lead.