Woods' knee couldn't withstand the force he put on it when he tried a hold shot.
The preferred shot under pressure for most tour pros is often what is called a "hold shot," or a "hold cut." The term refers to a downswing action in which a right-handed golfer executes a full body release with his right side, but holds off the counter-clockwise rotation of the clubhead through impact with a forceful bracing of the left leg and left wrist. The attraction of the shot is that when the throat gets tight and the hands get twitchy, it allows the player to still make a more nerve-resistant aggressive move with a reasonable safeguard that the much-reviled pull or pull-hook will not be produced. In effect the hold shot eliminates the left side of the golf course.
Arnold Palmer's follow-through was the manifestation of a hold shot in extremis. So is Jim Thorpe's. You may have noticed the way Ernie Els and Bernard Langer often invert their hands after impact so that the club shaft sort of twirls in front of their faces rather than more conventionally finishing over their left shoulder. They are hitting a hold shot.
The hold cut is a shot Tiger Woods often favors, but it's also one he had an increasingly difficult time relying on at the U.S. Open, especially with the longer clubs. Because his surgically repaired left knee was causing him so much pain, and also because the surrounding muscles are not as strong as they were pre-surgery, Woods couldn't be completely sure that his left leg would consistently resist all the force generated by his body turning against it when he went for the hold shot.
Robbing him of confidence right out of the box Sunday was his badly double-crossed drive off the first tee, which led to a double bogey. Later, his pull-hooked 3-wood second (when he was set up for a cut) to the par 5 13th -- at a moment when he was holding a one-stroke lead and aggressively seeking a championship-seizing birdie -- will go down as one of the least Woodsian of his career. And when it seemed imperative for Woods to get his drive in the fairway on Torrey Pines' 18th so he could be sure to reach the par 5 in two, his "hold cut" started too far left and didn't cut enough. After the round, Hank Haney said Woods' knee problem "took away one of his go-to shots." Haney was talking about Woods' impaired ability to hit the hold.