Australia rules, takes third straight Group One
Joseph O'Brien rides Australia (R) to victory in the Derby on Derby Day during the Epsom Derby Festival, in Surrey, on June 7, 2014 - by Carl Court
The Irish raider, who coasted to victory in both the Epsom and Irish Derbies earlier in the season, eased away in the final furlong under the trainer's son Joseph O'Brien to justify his odds of 8/13 on favourite.
Victory moves Aidan onto the same mark as Michael Stoute at the top of the trainer's table for victories in the race.
French Derby winner The Grey Gatsby ran on impressively to finish second two lengths adrift at 12/1 while the hotly-fancied Telescope flattered to deceive and found nothing in the final furlong to finish third at 5/1.
Aidan O'Brien, who became the first trainer to win three successive Epsom Derbies when Australia prevailed in June giving him his fifth victory in all, said he had felt his stable star was ready for a return to the racetrack.
"I felt he was ready for a racecourse gallop," said the 44-year-old.
"The important thing about him is his speed and I couldn't be happier with him today."
O'Brien, whose winner earns a free entry to the Breeder's Cup Turf with another option the Japan Cup, where he would pick up a bonus if he won that to add to the International Stakes, said Australia's long term campaign would be decided by him and the owners which includes former bookmaker Michael Tabor and the Coolmore Stud.
"In the immediacy the thought is to go to Leopardstown and the Irish Champion Stakes (September 8)," he said.
Joseph, whose constant battle with his weight could eventually see him have to change to becoming a national hunt jockey, said Australia had given him cause for concern early in the race which was raced over a shorter distance than the mile-and-a-half of the Derby.
"He was a bit fresh today but nevertheless the outcome was never in doubt," said the 21-year-old.
"He wasn't as explosive as he can be but it was still an impressive win."
Kevin Ryan, the trainer of The Grey Gatsby, was delighted with his runner's performance.
"I'm proud of him. We are very excited about our horse and he delivered a fantastic run with a great ride by 'Hughesie' (Richard Hughes)," he said.