As a three-year-old in 1904, he won both the 2000 Guineas Stakes and the Derby, but he failed to win the English Triple Crown when he was well beaten in the St. Leger by the filly Pretty Polly.

[6] He won a Rous Memorial Stakes at Newmarket in October, but later that month faced Pretty Polly again at the same course in the Middle Park Plate, regarded as the year's most important two-year-old race.

After tracking Henry The First in the early stages, he took the lead two furlongs out, pulled well clear and won easily, beating John O'Gaunt by four lengths.

St. Amant's temperament problems resurfaced in the Newmarket Stakes over ten furlongs on 12 May, in which he "declined to exert himself"[1] and finished third behind Henry The First and John O'Gaunt.

[12] The performance led some to question the colt's attitude and "courage", with one observer describing him as a "thorough rogue"[13] and his odds for the Derby drifted out from 9/4 favourite to 5/1.

[15] The race was run in a violent thunderstorm, which appeared to adversely affect some of the runners including Gouvernant and Henry The First but St. Amant broke quickly, opened up a clear lead, and was never headed.

[17] As part of the celebrations Rothschild distributed coal, groceries and money to the widows of Newmarket, and gave half a crown to every schoolchild in the neighborhood.

Pretty Polly was pursuing her own version of the Triple Crown, having won both of the fillies' classics and the first meeting between the pair since their two-year-old season was highly anticipated.

[19] St. Amant was sent to the front after two furlongs in an attempt to repeat the tactics employed at Epsom, but soon after half way he "began to sulk" and dropped back.

[25] At the end of the season St. Amant was sent to be exercised over hurdles at the stables of Tom Cannon Jr at Chattis Hill in Hampshire, in an attempt to "restore his courage".