Ceisteach edged out Kaleefa and Ode To Psyche in a pulsating climax to the Irish Stallion Farms European Breeders Fund Fillies Maiden at Leopardstown.
Jim Bolger's Ceisteach was a 7-1 shot having finished second and seventh on her two appearances as a juvenile, with the Dermot Weld-trained Kaleefa a well supported 7-2 chance for her racecourse debut.
As the pacesetting Laraaj weakened quickly from the home turn, the three who fought out the finish swiftly moved up to contest the lead.
Kaleefa looked to be travelling the best of the three early in the straight, but both Ceisteach and Ode To Psyche dug deep and there was little to choose between the trio as they passed the post.
After a brief wait the stewards called Ceisteach and Kevin Manning the winners by a nose from Kaleefa, with Ode To Psyche just a short-head further back.
Bolger said: "You always have a bit of luck on your side when you come out the right side of one of those (photo finishes).
"She'll go for some black type after that and she'll stay a mile and a half very well."
Kaleefa's trainer and jockey Dermot Weld and Pat Smullen swiftly gained compensation for the narrow reverse as Fascinating Rock ran out a decisive winner of the Bulmers Live At Leopardstown Summer Racedays 2014 Maiden.
The 9-1 shot finished ultimately well beaten on his racecourse debut at the Foxrock track in late October, but travelled like much the best horse in this mile and a quarter assignment on his seasonal reappearance.
Once popped the question by Smullen, Fascinating Rock quickly put the race to bed, sealing victory by a length from Adjusted, with 4-5 favourite Marakoush third.
Weld said: "It was a very pleasing performance from potentially a very nice horse. We'll see how he comes out of the race, but we were thinking if everything went according to plan he'd go for the Ballysax Stakes at Navan (April 12) next.
"It's maybe a little bit soon, but it's a Group race that's coming up for him and hopefully there is a lot of improvement in him. It was a nice performance there, but on better ground you might see an even better performance, as he's bred to want top of the ground.
"He's done very well over the winter and come forward, so he was the one horse we thought could be a bit of a surprise package this season."