Aidan O'Brien won the Racing Post Trophy for the fourth time in six years and Kevin Darley landed the Group One prize for the second successive season when they teamed up again to take the spoils with Brian Boru at Doncaster on Saturday.

The combination struck last year with High Chaparral, while in 1999 O'Brien sent out Aristotle to win under George Duffield, who rode the stable's Castle Gandolfo to finish second last year and was on board Powerscourt yesterday.

And Mick Kinane partnered Saratoga Springs to victory in the 1997 renewal.

It was a far from trouble-free race, and it looked as if Darley might have difficulty getting a clear run, but he managed to extricate Brian Boru from the rails and the Saddler's Wells colt, now 20 to 1 favourite for the 2003 Epsom Derby with Paddy Power, quickened up to collar stablemate Powerscourt inside the final furlong and edge away to score by one and a quarter lengths. Illustrator took third with O'Brien's The Great Gatsby in fourth.

The former's rider, Pat Eddery, said: "He has run a good race really, I followed the winner through and got a run when I wanted but he tired in the last half furlong."

O'Brien's assistant, TJ Comerford, was delighted with the one-two-four: "I have just spoken to Aidan in America (at the Breeders' Cup) and he was delighted with the horse, I rang him just before the race started and I commentated on it for him."

Darley is enjoying a tremendous season, this was his fourth Group One success in Britain to add to one in Canada, and he said: "I think Brian Boru is just a bit immature and his mind is not in gear yet, but I gave him one smack and that was all and he has the makings of a very good horse."

Duffield had no complaints, saying: "My horse has run a great race."