8. Phil Mickelson, 2006 U.S. Open
Mickelson started his career 0-for-46 in majors, then changed his approach. He dialed back the aggression and started making much better course management decisions. And it paid off: He entered the 2006 U.S. Open at Winged Foot going for his fourth career major and third in a row.
And he almost got it. But then he reverted to his previous form. His driver deserted him all through the final round (he even hit into a trash can on No. 17), yet he kept hitting it; and his decision-making deserted him on the final hole.
Mickelson had a 1-stroke lead as he stood on the 18th tee. Despite hitting only two fairways all day, he pulled the driver again. And again, he missed - only this time badly, his drive hitting the roof of a hospitality tent and bounding into the spectator area.
Mickelson had a decent lie, but a bad idea. Rather than advancing the ball a short distance but getting it back in the fairway - where he might make par the hard way, or, at worse, bogey to get into a playoff in which he'd be the heavy favorite - Mickelson attempted a huge slice under and around tree branches. It didn't work. The ball hit a branch and stopped 25 yards in front of him.
He hit another big slice, but this one plugged in a back bunker, and not even Mickelson's short-game magic could save him from there. He double-bogeyed and finished one shot out of a playoff.
"I am such an idiot," he succintly said afterward. http://golf.about.com/od/historyofgolf/a/worst_chokes.htm