As a three-year-old he won the Ballydoyle Stakes at Leopardstown Racecourse in April in workmanlike style but then created a 33/1 upset by winning the Royal Whip Stakes at the Curragh, beating his stable companion Valinsky who started favourite as well as the previous year's Irish St Leger winner, Meneval. Alleged then won the Gallinule Stakes and was originally scheduled to run in the Irish Derby, but Vincent O'Brien decided to run Epsom Derby winner The Minstrel instead and rested Alleged until August when he outclassed a strong field in the Great Voltigeur Stakes at York. Alleged started favourite for the St. Leger Stakes, but finished second to Dunfermline. Many observers felt that jockey Lester Piggott erred in taking on Dunfermline's two pacemakers throughout the race rather than conserving Alleged's stamina and using his superior finishing speed. In the 1977 Prix de l'Arc de Triomphe, Alleged led for most of the way and won readily by one and a half lengths from Balmerino, easily reversing placings with Dunfermline who finished fourth.