Great Heavens showed a tremendous turn of foot to take the Darley Irish Oaks in testing conditions at the Curragh.
The John Gosden-trained filly looked beaten two furlongs out as the pace quickened, with Shirocco Star tightening up Was at the head of affairs before seeing off the Epsom Oaks heroine.
William Buick pulled Great Heavens out for a run and once in the clear, she took off in tremendous style to zip past the field down the outside and beat Shirocco Star by three lengths.
The Dermot Weld-trained Ribblesdale winner Princess Highway could not quicken up in the ground and had to settle for third, with Was in fourth. The result remained unaltered after a stewards' inquiry, but Shirocco Star's jockey Johnny Murtagh picked up a two-day ban for careless riding.
Gosden said: "She got boxed in and with the draw on the inside it was never the intention to stay there. She showed a lot of class and a lot of courage - the ground is very holding, so it's not easy to pick up on that.
"I'd nearly given up hope at the two-furlong marker. I didn't think we'd get out, but she's got a lot of ability. She had to be asked a really big question in the last furlong and she went and opened up three lengths on the field, so I think it says a lot about her.
"She's actually put weight on between her races. She's one of those rare ones that seems to eat and do better - she's got a good temperament. It's not easy with this weather.
"She'll be freshened up now and then she'll be in races like the Yorkshire Oaks and she could also have an entry in the Leger. There's no reason a filly of her class couldn't do something like that - someone has got to take on Camelot."
Buick, who was celebrating his 24th birthday, added: "What a filly - that's certainly one of the best birthday presents I've ever had. It got a bit tricky halfway there and I was kind of cursing myself at one stage. She was the best horse by far in the race. She picks up and she quickens.
"She's a very good filly and I think people have underestimated her. It was a good training performance by John Gosden. She didn't really come to hand early in the season and he's just given her time and confidence and picked up nice races in between. She came here with her confidence sky high."