Comply Or Die has won the 2008 Grand National at Aintree
Jockey Timmy Murphy, jubilant after his horse's triumph, said: "I can't really believe it yet".
"It's the best ride I've ever had. He got into a lovely rhythm, jumped fantastic and picked up for me again when Paul Carberry came up to me. It hasn't sunk in yet."
Thousands of punters from across Northern Ireland were hoping local hero Tony McCoy would be first past the post but his mount Butler's Cabin fell as it negotiated the notoriously difficult course.
The Co Antrim-born champion jockey was among 40 runners and riders competing at Aintree this afternoon.
Favourites tipped with a winning chance before the race included Cloudy Lane, Comply or Die, Slim Pickings and Chelsea Harbour.
Bookmakers William Hill estimate £500,000 will be gambled across all sports this weekend in the UK for the first time ever.
Sean Lynch, trading manager from Ladbrokes Northern Ireland, said: "The buzz is starting to build up and we expect it to be non-stop. For the non-punter this is probably the biggest day in horse racing."
Yesterday, Mr Lynch said a lot of punters were placing their money on Tony McCoy to win.
"I think a lot of money will be put on Butler's Cabin by people from Northern Ireland, there is a lot of support for McCoy."
The 12-time champion jockey has failed to win the race and is desperate for a bit of luck.
"If you've been dominant in any sport and haven't won one of the big events, then it is seen as a bit of a failure," he told the BBC.
"So I would like to put that to bed as quickly as possible."