Antonio was one of only two classic winners produced by Thoroughbred family number 34, the other being his distant relative Birmingham who won the St Leger in 1830.

[3] Antonio began his racing career at Catterick Bridge Racecourse on 15 April 1819 when he was beaten by his only opponent Agricola in the Old Stakes over two miles.

[6] On 18 September, Antonio was one of nineteen colts and fillies to contest the forty-fourth running of the St Leger Stakes at Doncaster Racecourse.

Following the withdrawal of Sultan, who was injured on the morning of the race, the betting was headed by Henry Peirse's colt Wrangler, who started at odds of 7/4 ahead of Sir Walter and Agricola on 7/1.

[3] The affair led to calls for the starting procedure for major races to be reformed, with the use of a flag being strongly advocated to counter the tactical ploys of "cunning jockeys" who were thought to manipulate the existing rules to obtain an unfair advantage.

In July he met the "other" St Leger winner Sir Walter in the Corporation Gold Cup at Lancaster but the two four-year-olds were easily beaten by the nine-year-old Doctor Syntax.

[10] Later that month Antonio "won easy"[11] from his only opponent in a sweepstakes at Preston but at York Racecourse in August he was beaten by Wrangler in a division of the Great Subscription Purse.

On the following afternoon, Antonio won the Stand Cup at the same venue, beating Sir Thomas Stanley's Tarragon (the favourite) and three others[12] after what was described as "a fine race".