SAN FRANCISCO — Don’t think. Don’t feel. Just play. Look at your lie, no matter how brutal, evaluate your next shot, no matter how challenging and tell yourself, “Magnificent opportunity,” not, “Worldwide humiliation.”

Don’t look at the leader board too often. Don’t wonder: “What will it take to win this miserable, magnificent U.S. Open? Even par? Three under par? What’s everybody else doing? Collapsing? Charging? Is this one of those years when 5 over wins and if I just stop gagging my guts out I’ll win?”

At the U.S. Open, you absolutely never know what it will take to prevail. And if you think about it, you are automatically and invariably dead.

It you make three straight bogeys and all those familiar black-dog golf thoughts invade your soul and you think (even though you know you shouldn’t), “I’ve let my Open chance slip away,” then that thought itself — far more than those bogeys — becomes a self-fulfilling prophecy.

“There’s a fine line on this course between 67-68 and 75-76,” said Northern Ireland’s Graeme McDowell, who shot 68 on Saturday to tie Jim Furyk (70) for the U.S. Open lead at 1 under par, two shots ahead of Sweden’s Fredrik Jacobson. “I tried to be as unemotional as possible. Only allow two kinds of emotion — good ones and neutral.

“We’re all scared of messing up. We all have a fear of success or a fear of failure. I only have fear of failure,” said the 2010 champion at Pebble Beach, who says the Pacific sea air reminds him of his homeland. “I was nervous, anxious before the round. I had to get my head screwed back on right.”

On this glistening day, he did. Like a dozen others within four shots of the lead, he’ll have to begin that process of confronting failure all over again Sunday. On this course in particular, it’s essential to access in advance how much mortification is simply part of the price of a U.S. Open prize.

Perhaps there has never been a confidence-shredding U.S. Open course that has been so viciously set up to play on exactly this natural human tendency to quit too soon. The first six holes at the Olympic Club are probably the toughest opening stretch in the event’s history. On Thursday, five of them ranked first, second, third, fifth and sixth in difficulty on the course.

Almost as bad, there is only one birdie hole (No. 7) until you get to the 15th tee. Oh, the last mile is (relatively) a piece of cake with the 108-yard 15th hole, the back-to-back par-5 16th and 17th holes and a tiny, tricky, 344-yard 18th hole. But how many contenders will arrive there with their sanity, and their mathematical chances, still intact? After taking such a beating for so long for such high stakes, how many players can switch to attack mode?

In other words, that fine line between 67-68 and 75-76 is perilously real. But it is likely to be the middle of that range which proves most important.

Here is a partial list of players, within the last six years, who could have won outright, or gotten into a playoff, if they had simply carded an even-par round on the last day of this event: Tiger Woods (twice), Lee Westwood, Phil Mickelson (2 over would have won at Winged Foot), Bubba Watson (3 over would have won at Oakmont), Vijay Singh, Ernie Els, Gregory Havret, Steve Stricker, Colin Montgomery, Paul Casey, Justin Rose, Stephen Ames, Kenneth Ferrie and Ricky Barnes (3 over would have won).