BOSTON - The gangly young golfer in the photo superimposed on the floating island green in Boston Harbor on Wednesday looked nothing like the refined gentleman in the portrait over the fireplace in Barbara McLean's Cape Cod home.

But those diverse images - one of an awkward 20-year-old in wrinkled knickers, the other of a stately 58-year-old adorned in the red jacket awarded him as the first American captain of the Royal and Ancient Golf Club of St. Andrews - frame the astounding story of their subject, Francis Ouimet.

"It's almost too hard to believe, isn't it?" McLean, Ouimet's 92-year-old daughter, said last week at her home in Dennis, Mass. "What's more amazing is that we didn't know much about what our own father had done until he died [in 1967]. Daddy was very humble."

Though Ouimet rarely trumpeted his achievement, a century later it remains the cornerstone of American golf.

In September 1913, Ouimet, a poor gardener's son who taught himself what was then an upper-class game, transformed U.S. golf from pastime to passion.

With a feisty 10-year-old on his bag, on the Country Club of Brookline course that abutted his immigrant parents' home at 246 Clyde St., this ex-caddie upset the world's two greatest golfers, Britain's Harry Vardon and Ted Ray, to capture the U.S. Open.

Earlier this year when Golf World magazine chose its 18 most important moments in golf, Ouimet's win was No. 1. It was, then and now, the stuff of fairy tales.

"If his story were written as fiction, you still wouldn't believe it," Bill Paxton, the actor who directed The Greatest Game Ever Played, the 2005 Disney movie based on Mark Frost's book of the same name, said this week. "I hadn't been aware of it. But even when I read the script, I was still like, 'You've got to be kidding me. There's no way this is real.' "

While the two British stars had been winning tournaments and touring the world to promote golf, Ouimet had been caddying, practicing on crude backyard holes he'd created, playing a furtive hole or two at Brookline.

After his unthinkable victory, the number of golfing Americans ballooned in a decade from 350,000 to 2.1 million. There were 700 courses in 1913, 5,600 by 1929.

"Ouimet's win made golf in America," said Frost, who last week attended a gala here for the Ouimet Scholarship Fund. "No single event has meant more."

The upset will be recalled often in this centennial summer, especially when the 2013 U.S. Open takes place at Merion Golf Club in June. Ouimet played at the Ardmore course in both the 1924 and 1930 U.S. Amateurs, losing, 11 and 10, to eventual winner Bobby Jones in the '24 semifinals.

Meanwhile, the Boston area, where Ouimet spent his life, is commemorating the anniversary with numerous events, including Wednesday's fund-raiser, which drew 2,100 to the Boston Convention and Exhibition Center.

Earlier that day, the island green was temporarily installed in the murky water behind the Moakley Courthouse for a midday promotion that featured Arnold Palmer, the Ouimet centennial's honorary chairman.

Palmer and Ouimet, the men responsible for American golf's two great growth spurts, met in 1963, when the Open again was held at Brookline.

"He couldn't have been nicer," Palmer recalled. "I'd grown up knowing about the things he, Bobby Jones, and Walter Hagen had done. So it was a great thrill for me. That's why I'm flattered to be back here and to be able to help with the scholarship program."

At that '63 Open, which Palmer lost to Julius Boros in a playoff, the 70-year-old Ouimet watched from an isolated spot along the third hole, not wanting to attract attention.

Throughout the tournament, McLean recalled, her father would sneak in and depart from the club's rear entrance.

"He wasn't anti-social. He just couldn't understand why people wanted to make such a big deal about what he'd done," McLean said.

"He was just our father. He'd come home from work on the train every night and we'd have dinner just like any other family. We knew he loved golf, but he rarely talked it. It wasn't until after he died that people really explained it to us."

A self-taught golfer

Although a troubled young Philadelphian named Johnny McDermott had won the Open in 1911 and 1912, his accomplishments were diminished because those fields had not included Vardon or Ray.

When those two luminaries, scheduled for an American tour that summer, expressed interest in playing in 1913, organizers moved the event from June to September to accommodate them.

Today, near the Country Club of Brookline entrance, just out of view from the golfer's boyhood home, stands a statue depicting Ouimet and caddie Eddie Lowery trudging up a fairway. They resemble urban urchins hacking their way around a municipal layout.

Ouimet was no hacker. Growing up so close to the game, he'd taught himself golf by using balls he'd found on the course and clubs he'd been given by members.

At dusk, he'd often sneak onto the course, which one contemporary writer described as "rolling meadow land, thickly and prettily wooded, with every now and then a formidable rock that adds a touch of wilderness and romance."

"He was," McLean joked, "a 5 o'clock member."

To play a full 18 holes, Ouimet had to lug his clubs on three streetcars to reach the nearest public course, in Dorchester.

Working then in a Boston sporting goods store co-owned by Red Sox manager Harry Wright, Ouimet initially was not going to enter the '13 Open.

While he'd won that summer's Massachusetts Amateur, he shot 88s in two practice rounds at Wellesley Country Club, where Open qualifying was held. After his bosses arranged a September vacation, Ouimet qualified for the 66-man field.

He had wanted veteran caddie Jack Lowery to handle his bag. But when that youngster took ill, his 10-year-old brother, Eddie, asked Ouimet if he could substitute. Somehow the golfer agreed.

"Can you imagine?" said Eddie Lowery's daughter, Cynthia Wilcox, who also attended the scholarship event. "You're a 20-year-old playing in your first U.S. Open and your caddie is a 10-year-old boy?"

Lowery proved a godsend, loudly and frequently encouraging the laid-back Ouimet. Before particularly tough shots, when a relaxed grip was demanded, the boy would whisper to him, "Easy, squeezy, bourbon, pleasy."

Nearly everyone conceded the tournament to Vardon, who by then had won five British Opens, or Ray, who'd captured that prestigious event the previous year.

Vardon shot a 75 in the opening round, Ray a 79. Ouimet came in with a 77, which left him tied for 17th. After 36 holes, Vardon was tied for the lead, while Ray was 2 back and Ouimet 4 behind. After three rounds, this odd trio was tied at the top.

In round four, Ouimet chipped in for a birdie at 13, sank a long putt for another at 17, and parred the difficult 18th to tie his British counterparts and set up the historic Sunday playoff.

"Whoever wins," forecast Bernard Darwin, the British journalist who accompanied Ray and Vardon here, "there is only one hero of this Championship, and that one is Mr. Ouimet."

In a gloomy drizzle, before the largest American golf crowd to that point (10,000), Ouimet played smart and consistent golf.

Ray faded first, and then, with a costly bogey on 17, Vardon. When the 20-year-old wrapped up his victory with a par at the 18th, the normally sedate Country Club of Brookline erupted.

"A roar went up which shook the air and rumbled away for miles," the New York Tribune reported.

Women tossed flowers at Ouimet. Men hoisted the winner and his caddie onto their shoulders. More than $150 was collected for Lowery.

"You would think Daddy would have talked about that scene for the rest of his life," McLean said. "But he just wasn't that way."

The New York Times carried the news on its front page, and doors opened for Ouimet and his caddie.

An accomplished amateur player himself, Lowery moved to California, where he started several auto dealerships and became a prominent figure in West Coast golf. He died in 1984.

Ouimet, a successful stockbroker who raised his family in Wellesley, would win U.S. Amateurs in 1914 and 1931, reaching its semifinals in seven of 10 years. He was a member of the first Walker Cup team, playing or captaining in that event 12 times. Golf's Hall of Fame made him one of its four original inductees.

He golfed with presidents and British royalty, but, according to McLean, would have been just as happy playing with his butcher.

"He was no snob," she said. "He'd grown up poor."

Ouimet had an affinity for caddies, and the scholarship fund that bears his name was begun in 1948 to assist them. That first year, it awarded $4,600 in scholarships to 13 students. This year it will provide 263 students with $1.5 million in aid.

"The luckiest thing that ever happened to American golf," said famed golf writer Herbert Warren Wind, "was that its first hero was a person like Francis Ouimet."

So great was his reputation for sportsmanship that the NHL's Boston Bruins made him their president, baseball's Boston Braves their vice president.

In 1951, the R&A named him its first American captain. To commemorate the honor, Ouimet sat for a portrait by avid golfer and soon-to-be-president Dwight D. Eisenhower.

Eventually, the stuffy Country Club of Brookline even granted Ouimet membership.

"They made him an honorary member," said McLean, emphasizing the distinction. "And they didn't do that until after he'd won the Open."