Mucho Macho Man, trained by Katherine Ritvo and ridden by Gary Stevens, won the Breeders' Cup Classic at Santa Anita.
In a pulsating renewal of America's richest race, Aidan O'Brien's Declaration Of War ran a huge race to be a close third in a virtual blanket finish, with Will Take Charge just denied in second as Mucho Macho Man hung on to give 50-year-old Stevens a first win in the Classic.
Ritvo, meanwhile, was becoming the first lady to train a Classic victor.
Stevens' mount moved powerfully into contention at the top of the stretch as last year's winner Fort Larned cried enough, but Will Take Charge rattled home with Declaration Of War staying on again for Joseph O'Brien and it was desperately close at the line.
Mucho Macho Man, second 12 months ago, held on by a nose and a head, to complete a fairytale for Stevens, who only returned to race-riding this year after retirement which had seen him take up acting and punditry roles.
"It was an incredible run and we are delighted" - Aidan O'Brien
O'Brien said of Declaration Of War, who will now be retired: "It was a fantastic run, and it just goes to show how tough it is in the Classic. All credit to the lads for sending him over here.
"He jumped well. Joseph got a good position on the turn and he fought all the way to the line at the end.
"It was an incredible run and we are delighted.
"I thought Joseph did everything perfectly, it was a copybook ride really and the horse still kept coming and coming at the end.
"To do that on his first run on dirt was fantastic, but he is off to stud now and will make some stallion. He's one of the best-looking horses I've ever trained.
"He has speed, together with strength, which are great assets, as well as a fine constitution.
"All these things will serve him well when he takes up stallion duties."
A jubilant Stevens said: "This is a dream come true - I always said the one race missing in my career was the Breeders' Cup Classic.
"I didn't think I'd get one, and I sure didn't think it would come in 2013."