c. San Francisco Chronicle PEBBLE BEACH -- As a cluster of spectators watched Wednesday's practice round alongside the No. 10 fairway, one gentleman looked to his left, toward the green in the distance. Then he peered to his right, back toward the tee in the distance. Neither seemed especially close. 'This is a f---ing par-4?' he said incredulously. 'Are you kidding me?' Other holes at Pebble Beach wade in more attention, for their miniature length (No. 7) or rich history (No. 17) or climactic path along the coastline (No. 18). But no stretch will prove more important in deciding the outcome of this U.S. Open than Nos. 8, 9 and 10, demanding par-4s tucked into the middle of the layout. A player might not win the Open there, on the scenic bluffs above Carmel Beach. But he could lose it in a hurry -- in the rough, on the rocks, on the beach, in any number of ways. These holes are Pebble's answer to Amen Corner at Augusta National, a strikingly treacherous and picturesque sequence. Tom Watson's father, Ray, called Nos. 8-9-10 the 'best three par-4s in a row in the world,' back before the younger Watson made his first visit to Pebble. He soon came to agree with his dad's assessment. Today's players also understand the danger lurking once they complete No. 7, the dainty downhill par-3, and step onto the next tee. That was clear in the sarcasm in Paul Casey's voice when he was approached on the practice green and asked about the difficulty of Nos. 8-9-10. 'It's not that difficult if you hit the middle of the fairways and the middle of the greens, is it?' Casey said, a twinkle in his eye and smile on his face. Then he answered his own question: Yes, actually, it's even difficult from the middle of the fairway. The greens on these holes are not only small, they're stuffed perilously on the edge -- rocks and sand on the right, bunkers and gnarly rough on the left. Or, put another way: There's nowhere to bail out. Casey, an Englishman who has played all over the world, struggled to produce any adequate comparison. 'Nothing combines the beauty (ital) (i(and(/i((endital) difficulty of those holes,' he said. So, on the brink of today's opening round, a closer look: No. 8 (428 yards): It seemed so serene near the tee Wednesday -- waves lapping over the rocks, breeze blowing firmly, beach in the background. Then, arriving by the landing area, the three small, ominous signs came into view: 'Danger Steep Cliff.' Jack Nicklaus called it the 'greatest second shot in golf,' with players launching long approach shots over the cliff and water toward a tiny target. USGA officials made No. 8 more lethal by narrowing the fairway and pushing it right, toward the edge of that cliff. Players now aim farther left off the tee, creating an even longer second shot. 'You used to have a lot of room there,' Watson said. 'Now you have to think about putting the ball in the fairway.' No. 8 ranked as the second most difficult hole in the 2000 Open, with a scoring average of 4.534. No. 9 (505 yards): The view from this tee makes it seem as if the whole world is tilted toward the ocean. The fairway slopes severely from left to right, in a daunting, Olympic Club kind of way. Even with the new tee -- adding 50 yards since the '00 Open -- some big hitters blasted away during practice rounds, with the wind at their backs. Casey used his driver and wedge (as did Tiger Woods), because his tee shot reached the hill running across the fairway and then scooted another 40 to 50 yards. It's still a chore to make birdie and a relief to make par, given all the trouble around the green. This hole ranked as the hardest in '00, at 4.557. No. 10 (495 yards): Here, the problem begins as soon as a player departs the previous green. Wait, he needs to walk to the left? Away from the hole? Pebble Beach officials lengthened No. 10, too, adding another 35 to 50 yards. That complicates an already scary tee shot, with the fairway bending to the right (with the beach below). One marshal stationed on No. 10 said several shots Wednesday landed safely only to bounce along the fairway and tumble out of sight. No. 10 ranked as the fifth most difficult hole in '00 (4.383 average). It also caps a telling stretch, where Pebble might ruin some players' days. E-mail Ron Kroichick at rkroichicksfchronicle.com. 