Santiago was a 14th winner of the Dubai Duty Free Irish Derby for Aidan O'Brien - who trained the first four home in this year's Classic at the Curragh.
Santiago, successful in last week's Queen's Vase at Royal Ascot, justified 2-1 favouritism to win by a head from stablemate Tiger Moth, with Dawn Patrol third and Order Of Australia back in fourth.
Seamie Heffernan held Santiago up well off the pace in a race run in deteriorating conditions as the weather closed in.
But they swept through runners from two and a half furlongs out to take over from another O'Brien contender, Iberia, and went clear before holding off the significant late challenge delivered by Emmet McNamara on Tiger Moth.
The winning margin diminished towards the post, but Santiago stuck to the task well, passing the line a head in front.
