Siskin landed a first Irish 2,000 Guineas triumph for trainer Ger Lyons as the colt's stunning late burst saw off Aidan O'Brien's six hopefuls.
The 2-1 favourite looked badly positioned with two furlongs left but Colin Keane moved his mount to the outside to unleash a winning charge.
Unbeaten Siskin was one and three quarters lengths clear of O'Brien's 14-1 shot Vatican City at the Curragh.
O'Brien's Lope Y Fernandez, a 9-2 shot, was third but this was Lyons' day.
Owned by Khalid Abdullah, Siskin provided Lyons and Keane with a first Classic success and added to his Group One victory in the Phoenix Stakes over six furlongs at the Curragh as a juvenile.
The colt was locked in a pocket on the rail with two furlongs of the mile Classic to run, but Keane managed to get a run and once in the clear his mount quickened smartly to the front.
In what was a rough race, O'Brien's Vatican City also finished to some effect with Lope Y Fernandez, who got the first run and looked like being the winner at one stage, was another three-quarters of a length back.
Prior to his Phoenix Stakes win over six furlongs at the Curragh, Siskin had won the Group Two Railway stakes over the same course and distance.
He had been due to run in the Middle Park Stakes at Newmarket in September, but became unruly in the stalls and was withdrawn.
However, there were no such problems in Friday's Classic as he took victory in his first race in excess of six furlongs.
Lyons said the victory meant "everything".
"It means 30 years' hard graft for everybody - to win a Guineas was always my number one and hopefully it's the first of many.
"That was hard work and full credit to Colin Keane. You don't get a Guineas handed to you and they both stood up when it was needed. If there was a kink in that horse then he wasn't going to go through that gap.
"Colin is the best there is at the minute. He's only a kid and he's going to keep improving."