Iridessa (14/1) was an authoritative winner of the bet365 Fillies' Mile for Joseph O'Brien and Wayne Lordan.
The daughter of Ruler Of The World could be spotted travelling sweetly as 5/2 favourite Hermosa and the trailblazing Pretty Pollyanna (7/2) duelled approaching the furlong marker.
Finding room between the pair, Iridessa swept to the front and was kept up to her work to score by a length-and-a-half to hand O'Brien his first Group One winner in Britain.
"I couldn't say we expected her to win, but we always loved the filly and we expected her to run well," said the trainer.
"She did it well and Wayne gave her a great ride. She travelled well and I thought she quickened up well. We're delighted.
"She ran well in the Curragh in a very messy race and then got drawn almost widest of all at Leopardstown, so on her last two runs she never got a fair crack at it really. Today was a fairly-run race and she showed how good she is."
Hermosa took the runner-up spot three-quarters of a length in front of Pretty Pollyanna, who emerged with huge credit on her first run at a mile.
Aidan O'Brien said of Hermosa: "She ran a lovely race and we were delighted. We will train her for the Classics.
"I think she is versatile enough. That was good to firm ground today and I would say she would handle soft ground.
"I'm delighted for Joseph and she (Iridessa) is home-bred. I get great pleasure out of Joseph beating me, great pleasure.
"I half expect it now. We know how tough it is and how hard they work (at the yard). It's marvellous - he could well put me into retirement before too long!"
Classic cuts after ready win
O'Brien added: "She's definitely well entitled to line up in it (1000 Guineas). Being by Ruler Of The World, she's probably more of an Oaks filly, but we'll get today out of the way and worry about that when the time comes.
"We'll enjoy today and give her a nice break through the winter and dream about next year."
Sky Bet spokesman Michael Shinners said: "That was an impressive performance and she went through the race very strongly. With the trainer suggesting she was more of an Oaks filly I'd imagine the 16/1 could prove quite popular."
Pretty pleased despite defeat
Michael Bell was pleased with Pretty Pollyanna's effort in defeat.
He said: "That was a fantastic run, it was just a pity the Irish had to invade!
"She looked as though she got the trip and it opens up options for next year. It was her first time running beyond six furlongs, so it was a different style of racing, but she has run a very good race.
"It is early to say, but a (Guineas) trial would make sense as that would be over seven furlongs.
"I would say she would almost certainly run in a trial."