Aidan O'Brien became the first trainer to win three successive Epsom Derbys on Saturday as favourite Australia prevailed in a thrilling race.
Australia, ridden by O'Brien's 21-year-old son Joseph, repelled a late challenge by Kingston Hill (15/2) to take the honours at 11/8 while Romsdal was third at 20/1 in the 235th running of the 3200m event.
Australia, O'Brien's fifth winner in the race considered the 'blue riband of the turf', follows Camelot and Ruler of the World in giving the Irish trainer his hat-trick.
O'Brien as ever refused to take the accolades as his alone not even the record making him change his habit of sharing it with the team from the stables in County Tipperary.
"We're in a privileged position to have such horses," said O'Brien, who had said in May that Australia was the best horse he had ever prepared for the Derby including his sire Galileo who won in 2001.
"We said what we thought was always the case that he was very special. He showed it today.
"Joseph gave him a great ride."
O'Brien junior was in no doubt how good a horse Australia was.
"Horses don't come better than this one. He is the best I have ridden," said Joseph O'Brien, who rode Camelot to victory in 2012.
Two of the winner's four owners Michael Tabor and Sue Magnier also became the most successful owners in the race's history with six wins.
"When I was a young lad this achievement in becoming the most successful owner in Derby history would not even have been a distant dream," said Tabor, a former bookmaker.
For the winner's breeder Lord Derby, the race being named in honour of his family, it was a moment of pure joy as he became the first member of his family to breed the winner since the 1933 champion Hyperion.
"It has been so long since we bred the winner that I can't believe this has happened," said Lord Derby, whose extraordinary racemare and winner of the 2004 Oaks Ouija Board is the dam of Australia.
Romsdal, under champion jockey Richard Hughes, stayed on well for third to give Friday's Oaks winning trainer John Gosden another reason to flash one of his broad grins.
"He ran a great race and we will aim him at the St Leger in September," said Gosden, who won the Derby with Benny the Dip in 1997.
Earlier, remarkable French horse Cirrus des Aigles collected his sixth Group One win despite going lame halfway through the Coronation Cup.
The eight-year-old gelding, who is the all-time record prizemoney winner in Europe with almost STG6 million ($A11 million), came home clear under Belgian riding ace Christophe Soumillon to prevail and justify his favourite's odds of 10/11 on.
Fellow French raider Flintshire, trained by six-time Coronation Cup winner Andre Fabre, was second at 6/1 after briefly looking like posing a significant challenge before the winner pulled away.
Soumillon immediately jumped off the winner after passing the post sensing that not all was right with the horse.
"I felt early on that there was something wrong," said the 33-year-old.
"In the middle of the straight he changed his leg stride and he never usually does that."
Trainer Corine Barande-Barbe believed there wasn't too much wrong with her stable star.
"I'm so proud of him," she said.
"He's a very brave horse. He loves fighting and winning."