ARDMORE, Pa. -- Merion Golf Club hides a tiny jewel in the shadow of its stately clubhouse, slightly off the trail of the other holes, obscured by the storied 18th hole and its Ben Hogan plaque. It's the 13th hole, a tiny par-3 wedged into a corner of the course between Ardmore Avenue and a mass transit line.

The 13th hole is just 115 yards long. You can walk completely around it on a steamy day without breaking a sweat. From the grandstand behind the green (which, appropriately, is smaller than most of the other grandstands), fans can clearly make out the golfers in the driving area. The hole plays so quickly that it is easy to miss on television. There is not far to walk, and no one is there long.

The 13th hole looks like a neighborhood chip 'n' putt course on the map. You have to see it up close to appreciate the fiendish subtleties. The green rises like a muffin top from a circular moat of bunkers. The sand is deep, and the front bunker has a high lip that obscures the green from the player. The green is roughly bowl shaped, so pin placement is everything, and while U.S. Open caliber players typically avoid the bunkers, two putts are common.

The 13th hole typifies Merion. It is short and deceptive. It rewards and it punishes. On Saturday, I watched all 73 golfers play this microcosm of the U.S. Open to learn the secrets of the little hole that can cause big problems.

The Early Groups

Webb Simpson, Jamie Donaldson, and Hideki Matsuyama appear at 12:57 p.m. All three drop their tee shots in the wide, gentle, charitable-looking terrain behind and to the right of the pin. All three face makeable second-stroke putts, but none can birdie, with Simpson grazing the lip of the cup. All three players settle for par. The whole affair takes just nine minutes.

Sergio Garcia, Rickie Fowler, and Robert Karlsson are next. The crowd roars as Fowler lands his tee shot four feet from the whicker basket. Garcia's ball strikes the green and dies 15 feet from the cup. Karlsson disappears behind the lip of the sandy knoll in front of the green. Fowler birdies. Garcia pars. The invisible Karlsson produces a promising recovery shot, but he two-putts for bogey.

A lot was made of "Sergio hecklers" early in the week, most of it highly exaggerated. The crowd at the 13th hole is a little rowdy. Donaldson turned and scowled at an audible (and clearly facetious) "all you guys suck" remark while the prior group was on the course. But Garcia gets polite applause and a little "Go, Surge" encouragement. Fowler, meanwhile, gets hoary love. "I've got you in my pool, Rickie!" shouts one fan.

With his red and orange horizontal striped shirt and hair puffing from the sides of his cap, Bubba Watson looks like Joe Niekro circa 1980.He's another fan favorite, as is Adam Scott, two of whose pint-sized, Aussie-accented fans stand in front of their father just to my right. The older lad groans with a discouragement beyond his years as Scott's tee shot rolls far from the hole. Watson's tee shot is even further off mark, and neither player can convert a long putt. Bio Kim, the third member of their group, is the only one who birdies. "Let's go someplace else," the disappointed little joey tells his father.

As lesser known players roll through, news filters in from around the course. Tiger Woods and Rory McIlory birdie the first hole. McIlroy then drives his second-hole tee shot toward a neighborhood patio. Garcia uses ten shots -- TEN -- on the 15th hole that hates him. But the 13th hole makes its own heroes. Steve Alker comes within inches of a hole-in-one. Morten Orum Madsen birdies with a 30-foot putt. Madsen is an exception. Every 15-footer is an adventure, as the subtle topography around the cup takes its toll.

David Lingmerth's 13th hole experience typifies the state of play. He misses a hole-in-one by inches, earning a huge ovation, the ball rolling not three feet away from the basket. Then his putt rims out, and he opens his hands in the universal sign language for WTF? From SportsCenter to par in seconds.

Nothing Is Easy

The 13th hole is generally considered the easiest hole on an easy (by major tournament standards) course. But what does that mean?

In the first round, players averaged 2.7308 strokes on the hole. There were 51 birdies, 96 pars, nine bogies. Most of the bogies went to lesser-known players, with Watson (whose long driving skills on the 13th would only place him on the fairway of the first) as a notable exception. Tiger and Garcia each birdied it before getting into trouble on the 14th.

But the 13th got a little ornerier in the second round. Greens were soggy sponges on Thursday, remember, and a healthy plop near the basket could be counted on to not roll far. On Friday and Saturday morning, the 13th offered just 27 birdies and claimed 19 bogeys, plus a double bogey. Phil Mickelson found a bunker and bogeyed. Michael Thompson bogeyed, and he missed the cut by one stroke. The stroke average climbed to 2.9613.

For most top players, the 13th looked like a place to gain a stroke, and they needed it. The 14th through 18th holes produced 125 double bogeys or worse through two rounds. The 13th could never take such a toll, yet the hole underscored the misconception of Merion. Early-week talk of leaders finishing eight under was out the window the first time through the back nine. The easiest hole on this easy course was really an oasis of par, a solid birdie opportunity which could not be taken for granted, or a bogey that no one could afford.

Down the Stretch

Jason Day's arrival heralds the end of a long lull of lower-rung players. Day is one-under on the day, four strokes off the lead at this point. His tee shot takes a familiar path: it lands behind the hole and rolls back, but to the right, resting in a groove that has become a waiting room for two-putts. But Day birdies: a precious shot gained on a bunched leaderboard.

Ed Loar enters the 13th one-over, several strokes off the pace. His tee shot takes Day's road-well-traveled into the groove to the right. His long putt misses inches left. Group-mates Padraig Harrington and Russell Knox miss even shorter birdie putts. Merion's easiest hole offers no charity as the crowds around the ropes swell; Tiger and McIlory, fighting for their lives, are on the tenth.

Michael Kim, a collegian who looks young enough to get carded for buying a Twilight novel, sinks a four-footer for birdie that puts him two strokes off the led. Ernie Els, whose car has tires older than Michael Kim, finds a strip of high fescue between two sandpits on the right. Els' recovery bubbles off his club and misses the cup by inches, rolling dead a few feet away. His putt is no gimmie; it takes all his experience to save par. The galleries behind the green ropes are now eight deep.

The King and his Court arrive, a combined 11 over par on the day. ESPN Radio has abandoned Tiger to focus on the leaders, which is remarkable. McIlroy and the third guy hit drives that follow the well-worn path into the right groove. Tiger's tee shot does not even do that much; it lingers and stalls behind the pin, down a tiny slope. His long putt hooks around the cup. McIlroy also settles for par. Only the other guy -- Gonzalo Fernandez-Castano, whose name appears something like FNDZ-CASTNO on the scoreboards -- birdies.

The tournament leaders fare little better. Charl Schwartzel arrives in the lead, three-under for the day, but he needs an up-and-down for par, chipping the ball a foot or two from the rough to the green to set up his putt. Hunter Mahan, red-hot on arrival, birdies to get under par for the day and the Open. Steve Stricker, usually a master of the short game, pars. Nicolas Colsaerts bogeys. The two-stroke different results in a swap of places between Mahan and Colsaerts near the top of the leaderboard. It could make a difference for them in the Open.

The leader group wraps the day at the hole. Phil Mickelson does what perhaps two dozen players did before him: drops the tee shot behind the hole, watches as it dribbles to the right. Billy Horschel rolls his ball a little in front of Lefty, Luke Donald a little in front of Horschel, as if they were all parallel parking. Lefty's attempt at birdie misses by six inches. Donald's short putt misses. Horschel birdies, and it gets him to 1-over for the day.

At the End of the Day

Michael Kim faded, with a double bogey on the 17th (another par-3) and two other late bogeys to finish one-over for the day, +4 for the Open. Day also had a late bogey but finished two-under, +2 overall.

McIlory finished five over, +8 overall; Woods was a stroke back, six over for the round, +9 overall. Of the early group, only Rickie Fowler did any real ladder climbing, his birdie on 13th helping him to finish three-under, +3 overall. Bubba Watson finished even for the day, +7 overall. Goofus and Gallant, Sergio Garcia and Webb Simpson, both shot five-over and were at +11 overall. Lefty somehow slipped to the top of the leaderboard with an even performance, -1 overall, with Mahan, Stricker and Schwartzel a stroke behind him

And the 13th hole? She claimed only four bogeys and offered 24 birdies after the cut took away many of the field's erratic players. Her stroke average was 2.7260, a relative cinch. She gave fans a show and many of the leaders a few strokes. Only Colsaerts got saddled with a bogey among the top players. But every par was a missed opportunity for the likes of Lefty, Schwartzel, Donald and Stricker, huddled at the top of the board. Follow with a double bogey or two, as Kim, Garcia and Henrik Stenson did, and those 15-foot putts that looked so easy become moments to regret.

That's the 13th hole's role. Other holes punish, but the 13th is flypaper. Players come expecting a stroke, and they get stuck. The bowl-shaped green with its bracelet of bunkers and strange little grooves is just one nasty, delightful surprise in a course full of them. Players may birdie the 13th in the final round, but they sure as heck will not disrespect it.