Updated

By Steve Keating

INDIANAPOLIS (Reuters) - Briton Dan Wheldon won the Indianapolis 500 on its 100th anniversary in stunning fashion on Sunday, claiming an unlikely victory after rookie J.R. Hildebrand crashed into the wall within sight of the finish line.

Driving a camouflage painted National Guard-sponsored car on the U.S. Memorial holiday weekend, Hildebrand had been poised to deliver a popular American victory for the nearly 300,000 sun-kissed spectators.

However, the cheers turned to gasps of disbelief as Hildebrand lost control coming out of the final corner and skidded across the finish line in second place.

It marked only the second time that a driver had surrendered the lead of the Indianapolis 500 on the last lap.

American Graham Rahal, son of 1986 Indy 500 winner Bobby Rahal, finished in third.

"There was a bunch of marbles on the outside and once I got up there, there wasn't much I could do," a dejected Hildebrand told reporters.

"As a driver I'm smart enough to not expect that I'm going to be in position to win the Indianapolis 500 my first race but, as it turned out, we were and we probably should have won the race.

"It's a helpless feeling when you get in a situation like that. It was my mistake."

Wheldon, runner-up here for the last two years, had been resigned to a third straight second place finish at the Brickyard but instead was gifted a second victory as his car charged past Hildebrand's wreck.

It was the only time during the race that Wheldon was in front, the Briton becoming the first driver to win the 500 having only led for one lap.

TEARFUL WHELDON

Wheldon, who arrived at the Indy without a full-time ride and a one-race contract with Panther Racing that was to expire at midnight, pulled his car into Victory Lane and burst into tears as he chugged from the traditional quart of milk.

"I just felt a lot of relief," said Wheldon, who won his first Indy 500 in 2005. "Obviously I knew he was okay because I could see him moving.

"It's an incredible feeling. I've been runner-up here the two years before this and never gave up. I was just trying to go as hard as I could.

"I knew it was the last lap and they said that a lot of those guys were struggling on fuel. I just kept pushing."

The wild finish is sure to be remembered as one of the most startling in the 500's long history and it provided a fitting climax to the race's centennial.

The Indianapolis Motor Speedway does not announce attendance but the grandstands that line the sprawling 2.5 mile oval were packed from early in the morning as fans soaked up the atmosphere and the sun.

The speedway paid homage to the 500's past during pre-race festivities, the Marmon Wasp driven to victory by Ray Harroun at the first Indy leading the parade lap with Parnelli Jones, the second oldest surviving winner of the race, at the wheel.

Until the dramatic finish, the centennial had been mostly uneventful, as Ganassi team mates Scott Dixon of New Zealand and defending champion Dario Franchitti of Britain set the pace.

But 50 laps from the finish, the race seemed to turn into a free-for-all.

Rahal, trying to match his father's feat 25 years earlier, briefly charged into the lead before Danica Patrick emerged from the pack to make a challenge.

The only woman to ever lead an Indy 500 was in front with 20 laps to go but Patrick had to pit for fuel, handing the spotlight to Belgian Bertrand Baguette until he too was forced into the pits with four laps remaining, leaving Hildebrand in front.

(Editing by Mark Lamport-Stokes)