Medicine Jack put up a game display to outpoint Peace Envoy in the GAIN Railway Stakes at the Curragh.
The leading pair were separated across the track but though Peace Envoy had the rail, Medicine Jack galloped on resolutely in the centre of the course to come out on top.
The early pace was set by Mirdif but there were plenty in with chances in the final quarter-mile.
Peace Envoy looked to hold a narrow lead under Ryan Moore in a bid to give trainer Aidan O'Brien a 13th success in Group Two contest.
However, the Ger Lyons-trained Medicine Jack (6-1) found more for Colin Keane and got the verdict by half a length.
Dream Of Dreams, trained in North Yorkshire, by Kevin Ryan, was a length and a half away with third.
It was a welcome change of fortune for Keane, who was involved in a nasty-looking incident earlier on the card when his mount Elusive Heights was brought down.