Billed as "The Greatest Spectacle in Racing," the Indy 500 lived up to the hype with a heart-stopping finish as Hunter-Reay beat Castroneves to the checkered by less than a car length to become the first American winner since Sam Hornish in 2006.
"I've been watching this race since I was in diapers sitting on the floor ... I'm thrilled," said Hunter-Reay after chugging from the traditional quart of cold milk in Victory Lane. "This is American history this race, an American tradition."
Staged on the U.S. Memorial Day holiday weekend, the Indy 500 may indeed be a uniquely American event but it had taken on an international flair with only two homegrown drivers reaching Victory Lane since 1998.
Hunter-Reay, who started the race well back on the 33-car grid, did not look to be the American driver to end that drought as the race got off to a blistering pace going a record 149 laps without a yellow.
But the 2012 IndyCar champion methodically worked his way through the pack and when a heavy crash by Townsend Bell sprayed debris across the track to bring out the red flag with 10 laps to run the 33-year-old was suddenly in position to take the win.
When the race was restarted with a seething crowd of 250,000 on its feet, Hunter-Reay and Castroneves staged a dramatic two-car duel by swapping the lead over the final six laps.
Stalking Castroneves, Hunter-Reay made the decisive move entering the final lap surging to the front then won a drag race with the Brazilian down the home stretch before punching his fist into the air as he crossed the famous yard of bricks.
It marked the first time in five years the race had finished under green, the previous four all ending under caution.
"Second place kind of sucks but taking the positive out of this, it was a great race," said Castroneves.
"I think both of us used every inch of the track ... at the end of the day there is stupid and then there's bravery. I think we're right there on the edge, both of us, really trying."
Hunter-Reay's Andretti Autosport team mate, Marco Andretti, trying to become the first member of the Andretti clan to reach Victory Lane since his grandfather Mario Andretti in 1969, finished third.
Adding to a spectacular day for Andretti Autosport was Colombian Carlos Munoz, who followed his team mate home in fourth, just ahead of compatriot Juan Pablo Montoya, who was racing his first 500 since winning 14 years ago.
Kurt Busch, the 2004 NASCAR Cup champion making his Indy debut, finished sixth but had little time to savour a brilliant result as he immediately flew to Charlotte where he will race NASCAR's Coca-Cola 600.
Canada's Jacques Villeneuve, back racing in the 500 for the first time since he won the race 19 years ago, finished 14th while Briton Pippa Mann, the only woman in this year's field, was 24th.
Local favourite Ed Carpenter, starting from pole for the second consecutive year, led the field into the first turn but it was Canadian James Hinchcliffe powering into the lead.
The first half of the race was one of the most uneventful as drivers set a record pace reaching the midway mark of the 200 laps without a single caution and only one retirement.
With the laps counting down it appeared for a moment the 500 might get to finish without caution until Charlie Kimball spun into the wall on lap 149 bringing out the first yellow.
The incident ended a remarkable run of error-free racing shattering the previous record of 66 laps without a caution.
The finish of the race, however, was far different as the favourites made their moves, Carpenter, Hinchcliffe and Scott Dixon all crashing out of the race.
Dixon, the 2008 winner, spun into the wall to end his day while Carpenter and Hinchcliffe came together with 24 laps to run wrecking both cars before Bell slammed into barrier setting the stage for the dramatic finish.
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