Originally trained in Ireland he showed modest ability in his early career but improved steadily and recorded his first big win as a four-year-old when he took the Ascot Stakes.
Eddie Ahern, who became the horse's regular jockey over the next two years, took the ride when San Sebastian recorded his first success in a small race over eleven furlongs at Sligo Racecourse on 1 June.
[7] San Sebastian won his next three races, taking minor events over thirteen furlongs at Wexford Racecourse in July and August before coming home five lengths of his rivals at Cork on 11 October.
On his first run as a four-year-old San Sebastian crossed the line in front in a handicap at Cork on 13 April but was relegated to second after the racecourse stewards ruled that he had hampered the runner-up Archive Footage by hanging to the left in the closing stages.
At Gowran Park on 30 May he belatedly opened his winning account for the year as he won "easily" by two lengths from Broken Rites when carrying 130 pounds in a fourteen furlong handicap.
After being restrained towards the rear of the field he began to make steady progress six furlongs out, overtook the favourite Rainbow Frontier in the straight and drew away to win by four lengths.
[11] After finishing first in eight of his last nine races, San Sebastian was strongly fancied when he returned from a break of over three months to contest the Group 1 Prix du Cadran over 4000 metres at Longchamp Racecourse on 3 October.
He tracked the leaders before taking the lead two furlongs out and held off the sustained challenge of Jaseur to win by a neck with five lengths back to the Doncaster Cup winner Canon Can in third place.
He came home fourth behind Kayf Tara, Far Cry and Compton Ace after being hampered by the winner a furlong out in an incident which saw his jockey Damien Oliver drop his whip.
The Aga Khan's entry of Enzeli and Tajoun was made ods-on favourite while the other runners included Royal Rebel, Persian Punch, Churlish Charm (Yorkshire Cup) and Three Cheers (Prix de Lutèce).
San Sebastian began to make progress in the straight, overhauled Persian Punch 100 metres from the finish and won by half a length with Royal Rebel, Churlish Charm, Enzeli and Tajoun just behind.
On hearing of the horses's death John Dunlop recalled "He made you laugh because he didn't do a tap and it was funny to watch him and our other senior stayer, Orchestra Stall, coming up the gallops like two old gents".