A Budweiser Irish Derby that had been billed as a coronation for the French superstar Dalakhani instead turned into a triumphant battle won by Alamshar and jockey John Murtagh.

Both colts are owned by the Aga Khan but the finish was anything but a team game as the Irish horse edged out the 4 to 7 favourite by half a length in a titanic battle.

Back in third was the 150 to 1 outsider Roosevelt, who emerged as best of the six Aidan O'Brien-trained runners, but yesterday was all about Alamshar, who on Friday had been a doubtful runner.

"It has been a wonderful team effort to get the horse here. I was very worried on Friday that he wouldn't be able to run," said trainer John Oxx. "But I had a feeling that it would come down to a battle between the two and our horse has tremendous courage."

An exuberant Murtagh, heavily criticised for his classic ride on Six Perfections in last month's 1,000 Guineas, milked the applause from the 31,136-strong crowd.

As he did so, Dalakhani and a despondent Christophe Soumillon returned to a lonely number two spot, and some tactical questions.

The Belgian-born rider had Dalakhani racing prominently in third place for much of the race and the hectic pace cut out by a pair of O'Brien outsiders resulted in the third-fastest time in the history of the Derby.

Soumillon (22), the young star of French racing, had been heavily featured in the media in the run-up but afterwards declared: "Too many interviews. It is unlucky."

Murtagh was understandably more loquacious and drew comparisons to the 2000 Derby winner, Sinndar, who was also trained by Oxx and owned by the Aga Khan.

"He is a lot like Sinndar in many ways. He is a bit smaller but very tough and he is a special little horse now. They went a very fast pace but once I got upsides Dalakhani my horse dug deep. When he went a neck up I knew I wasn't going to get beat," he said.

Alamshar was a fifth Derby triumph for the Aga Khan, which equals the total of his grandfather. However, his two star horses will follow different career paths from now on.

"They have different attitudes. Alamshar is a horse that likes fast ground and the plan has always been to run in the King George.

"Dalakhani is probably an autumn horse and the Prix de l'Arc de Triomphe is a logical autumn target. But they are two very good horses and I am happy with the result," the Aga said.

The third favourite, The Great Gatsby, runner-up in the Epsom Derby, could only manage fifth yesterday and jockey Michael Kinane said: "It looks like Epsom has taken its toll."

Kinane and O'Brien did, however, have two winners on the card, including the hot favourite, Antonius Pius, in the Group Two Railway Stakes.