Minoru began his racing career impressively, by winning the five furlong Great Surrey Foal Stakes at Epsom, on 5 June, the day that Signorinetta won The Oaks.

"[5] During the winter of 1908–1909, Minoru made exceptional progress, and although the King's racing manager, Marcus Beresford, was initially sceptical, Marsh decided to train the colt for the Classics.

The cold weather early in the year delayed the preparation of many horses, including Bayardo, but the lightly-made Minoru took little work to reach peak fitness, giving him an advantage over most of his rivals.

[6] After performing impressively in a private trial race, Minoru made his debut in the Greenham Stakes at Newbury on 31 March and won from Valens under top weight of 136 pounds.

At this point the race changed completely as Sir Martin, who had been traveling extremely well, stumbled in close quarters and lost his rider, badly interfering with William the Fourth.

The two colts crossed the line together, just ahead of William the Fourth who finished very strongly after recovering from the earlier incident, and looked an unlucky loser.

The victory for the "Royal" colt provoked "the wildest scenes of enthusiasm ever known in England",[13] including a mass rendition of the National Anthem as the King led his horse to the winner's enclosure.

[15] Minoru himself was "swallowed up" by a crowd of supporters, several of whom attempted to obtain souvenirs by pulling hairs from his mane and tail,[16] while his owner was informally congratulated with cries of "Good for you old sport!"

"[19] Minoru followed up his win at Epsom by running in the St. James's Palace Stakes over one mile at Royal Ascot, in which he started at odds of 1/3 and won from The Story and Blankney II.

[24] On his final start of the season, he was sent to Newmarket in October for the Free Handicap, in which he defeated the filly Electra, the winner of the 1000 Guineas and Epsom Oaks, by a neck.

As Jones had been injured the previous day,[25] Minoru was ridden on this occasion by Danny Maher, who was presented by the King with a jewelled scarf-pin in recognition of his success.

He made his debut in the City and Suburban Handicap at Epsom on 26 April and started 3/1 favourite, but finished seventh of the fourteen runners behind Bachelor's Double.

[30] The King's death resulted in the cancellation of all sporting events, including a meeting at Kempton Park Racecourse, where Minoru had been entered in the Jubilee Stakes.