Aidan O'Brien's Ballydoyle Stable continued its big fall push Saturday by winning the Seabiscuit St. Leger (Eng-I) at Doncaster, giving jockey Jamie Spencer his first victory in a British Classic.Brian Boru, the 5-4 favorite who was wearing the familiar silks of Mr. and Mrs. John Magnier, was last with a half-mile to run over the good turf. After making his move and battling head-to-head with 8-1 shot High Accolade down the long stretch, he eased clear to win by 1 1/4 lengths. Phoenix Reach was another 1 1/2 lengths back in third, with Maharib fourth.Brian Boru's victory made him the sixth Irish-trained winner of the world's oldest Classic. "He gave him a great ride and put him to sleep," said O'Brien.The St. Leger was Brian Boru's second group I victory, he having won the Racing Post Trophy last October.In the past week, O'Brien has won the St. Leger in England, the Irish Champion Stakes (Ire-I) in Ireland, and finished second in the Woodward Stakes (gr. I) in the U.S. and Grosser Bugatti Preis (Ger-I) in Germany.