The first serious clue that Sinndar might be Classic material came in the 1999 running of the Aga Khan Studs National Stakes at The Curragh. Here he pounced late to beat Murawwi and was full of running at the finish of a historic Group I race whose list of past winners included such turf immortals as Barcaldine, Americus Girl, Grand Parade, Santa Claus, Sir Ivor, Roberto and El Gran Senor. He wintered well, but his first two runs at three, a narrow defeat by the race fit Grand Finale, who was receiving 7lbs, in the Ballysax Stakes at Leopardstown in mid April, and a month later, his head defeat of Bach (received 7lbs) in the Derrinstown Stud Derby Trial Stakes, masked his real ability.

The Grand Lodge colt matured as the season continued and he transformed into a formidable racing athlete. This was to be demonstrated when he became trainer John Oxx's first Vodafone Derby runner. In the lead up to the race John, a man never given to exaggeration, was adamant that, in Sinndar, he was fielding a candidate with the ideal temperament for the hurly burly of Epsom and one that, having acquired experience in "proper races", only needed a true run contest to have a shout in the final tussle.

Sinndar, having completed the unique record of winning the Epsom Derby, the Irish Derby and the Arc de Triomphe.

And so it transpired, for after Johnny Murtagh had got him settled early on, he rounded Tattenham Corner lying 4th to Best Of The Bests. Sakhee had broken clear of the pursuing pack two furlongs out, but when asked to lay down his challenge, Sinndar kept finding extra to overhaul the leader and win by a length. The form of this vintage Derby has subsequently been franked by Sakhee recording prodigious 2001 victories in both the Juddmonte International Stakes (winning by nine lengths) and the Prix de l'Arc de Triomphe (by six lengths).

Sinndar became the fourteenth post-war winner of the National Stakes to secure an English or Irish Classic in the following season. Of the others, only Santa Claus had won two Derbys, but the Aga Khan, having successfully completed the double with his three previous Epsom winners Shergar, Shahrastani and Kahyasi, now asked Sinndar to emulate Santa Claus. It was to be a unique renewal of the Budweiser Irish Derby in that His Highness's colours were in the lead all the way. Sinndar's stablemates Raypour and Takali occupied first and second spots for the first ten furlongs, but once Murtagh produced the favourite, he showed great power to go clear and win by nine lengths from Aidan O'Brien's pair Glyndebourne and Ciro, after them came Raypour (fourth), Takali (fifth) and the Prix du Jockey-Club winner Holding Court (sixth).

No horse had ever won two Derbys and the Prix de l'Arc de Triomphe in the same year and this was the target the Aga Khan set Sinndar in the aftermath of his Curragh triumph. Given a brief lay off by John Oxx, the Prix Niel was picked for his preparatory race, this being an acknowledged Arc trial over the same course and distance. His pacemaker Raypour did the business and Sinndar showed that if anything he was a better horse in the Autumn than at the height of the Summer winning eased down by eight lengths from Crimson Quest. All was now set up for a serious clash with Montjeu, the previous year's Arc winner. A smaller than usual field of ten runners might have been expected to work against Sinndar and Montjeu held the call on the Pari Mutual. However, Raypour who had been supplemented saw to it that this was a true run contest and Montjeu was always being held as Sinndar was ridden clear to beat the Prix de Diane winner Egyptband by one and a half lengths. His time of 2 minutes 25.8 seconds has only once been bettered in the history of the race.