Australia won the 235th running of the Derby at Epsom as jockey Joseph O'Brien helped his Irish trainer father Aidan create racing history.
The 11-8 favourite travelled beautifully and triumphed from runner-up Kingston Hill as O'Brien senior became the first trainer to saddle the winner three years running.
Scoring by a length and a quarter, Australia was roared home by a crowd of more than 100,000 with Romsdal back in third.
After the victory O'Brien senior said: "It's special to train three successive Derby winners, but we are very lucky to have such well bred horses to handle - that's the reality of it.
"A long time ago we thought he was very special - we wanted to be here with him, but you can never be sure because there are so many variables. Things can go wrong so big credit to everyone at home."
Australia justified his high-class breeding as a son of 2001 Derby winner Galileo and 2004 Epsom Oaks victor Ouija Board.
But O'Brien had indicated before the race that he considered the colt to be the best he has ever trained.
O'Brien's 21-year-old son, winning his second Derby after Camelot's victory in the famous Classic, had his mount positioned perfectly throughout.
He swept to the lead coming down the hill and accelerated in fine style to land another victory for the Coolmore owners of Sue Magnier, Michael Tabor and Derrick Smith. The fourth and final owner of Australia is Teo Ah King, the first time a Malaysian has held a share in the Derby winner.
The winning jockey said on Channel 4: "Horses don't come any easier to ride than this one. He's the best."
The 2014 winner has a link to the 12th Earl of Derby, whose name was given to the Classic in 1780. His descendant, the 19th Lord Derby, bred Australia.
Earlier, Cirrus Des Aigles - ridden by Christophe Soumillon for French trainer Corine Barande Barbe - secured a stirring success in the Group One Coronation Cup.
The eight-year-old gelding won by two lengths from Flintshire in the race run in commemoration of St Nicholas Abbey, the triple winner who died in January.
There was a poignant victory in the opening race on Derby Day for jockey Jimmy Fortune, whose wife Jan died aged three weeks ago aged 53 from a brain aneurysm, leaving behind her husband and two sons.
After winning on 9-1 chance What About Carlo, trained by Eve Johnson-Houghton, Fortune said: "It's been a tough couple of weeks but life goes on and Jan would understand."
Frankie Dettori - without a ride in the Derby for the third year running - enjoyed his first win at the Epsom meeting since returning from a six-month drugs ban a year ago when scoring with 15-8 favourite Baith Alga for trainer Richard Hannon in the Woodcote Stakes.