In 1966 at Olympic Club, Palmer had a 7-shot lead in the final round - and lost.
Palmer started the fourth round three shots better than Billy Casper, and when the players made the turn, Palmer had stretched his lead to seven strokes.
But then Casper went on a tear (he'd shoot 32 on the back nine) and Palmer cooled off. Arnie gave up a stroke at the 10th, then lost another at the 13th. The players halved the 14th, so to speak, which left Palmer with a 5-stroke lead with four holes to play.
And Casper completely erased that lead over the next three holes. Palmer gave two back at the 15th, then gave up another two on the 16th. When Palmer bogeyed the 17th, the entire seven-stroke lead was gone. Palmer and Casper were tied.
Palmer staggered home but managed to tie Casper on the 18th, forcing an 18-hole playoff the following day.
And once again, in the playoff, Palmer let a lead slip away. Arnie was up by two in the playoff with eight holes to go, but gave up six shots over the remaining holes. Casper won the playoff, 69 to 73, and the U.S. Open.
Palmer didn't play as poorly, overall, in the fourth round of the 1966 U.S. Open as did Greg Norman at the 1996 Masters. Norman shot 78 that day, while Palmer posted the very respectable score of 71.
Billy Casper deserves a tremendous amount of credit for winning this championship—probably more credit for winning the title than Palmer deserves blame for losing it. Casper went out and shot a 68, with a sizzling 32 on the back nine.
But Arnie? Losing a seven-shot lead over the final nine holes of a U.S. Open?
That's the biggest collapse in the history of golf...