Sue Smith’s 11-year-old claimed the world’s most famous steeplechase by nine lengths to line the layers’ pockets.
Seabass, third last year, was backed down to 11-2 favourite but was well down the field in 13th for Ted and Katie Walsh, while other leading fancies On His Own, Colbert Station and Imperial Commander failed to complete the course.
Coral’s David Stevens said: “There was a huge nationwide gamble on Seabass and Katie Walsh becoming the first female winner of the world’s most famous race, and a win for the pair would have cost the bookies tens of millions.
“Teaforthree and Imperial Commander were also extremely popular choices, but we have been saved by one of the biggest shocks in recent Grand National history, with Auroras Encore’s victory almost as good as the 100-1 success of Mon Mome in 2009.
“The race proved more popular than ever, and we estimate that two thirds of the adult population placed a bet, adding up to more than £150million staked across the UK.
“Luckily for us on this occasion, the punting Gods were smiling on the bookies, and delivered one of the best results we can remember.”
David Williams of Ladbrokes said: “It was a result beyond our wildest dreams. The winner seemed to slip off every radar.
“We thought Mon Mome’s victory a few years ago was superb but this was every bit as good.
“Turnover went through the roof as the nation came out for its annual flutter. The race is once again in rude health and the sun shone on the bookies at Aintree.”
Rory Jiwani admitted the team at Stan James feared the worst when strongly-backed Welsh runner Teaforthree (10-1) made his move at the top of the home straight.
Jiwani said: “There were more then a few nerves shredded in the office as Teaforthree moved ominously into contention.
“He and Imperial Commander were the only big losers in our book but 66-1 shot Auroras Encore swept past under Ryan Mania to the delight of us bookies.
“Many congratulations to Sue and Harvey Smith on training a Grand National winner but the best news of all is that there were no injuries to horses or jockeys.
“It was a superb race which will hopefully allay fears about the future of the National.”
William Hill spokeswoman Kate Miller claimed bets from 135 nations were placed on the race with the firm, compared to 86 in 2012.
* Jenny Pitman has hailed the achievement of Sue Smith in becoming only the third female in history to train the John Smith’s Grand National winner.
Pitman became the first lady to train a winner of the Aintree spectacular when Corbiere won the race in 1983, and she went on to saddle a second winner with Royal Athlete in 1995.
Venetia Williams struck gold with 100-1 shot Mon Mome in 2009.
Pitman told BBC Radio Five Live: “We’ve known Sue and Harvey for donkeys years and if ever justice was done, yesterday it was, as they so deserved this winner.
“There would not be one person in the horse industry as a whole that wouldn’t have been chuffed about the result.
“They put their heart and soul into everything they do, they’re horse people through and through.”