Her previous seven wins had come at shorter distances, but she had no problem staying the mile and a quarter for trainer Roger Charlton and jockey George Baker.
Last year’s winner Ambivalent tried to lead all the way but she was stalked by Venus De Milo, who went on early in the straight.
That move was covered by Baker on Thistle Bird (4-1), who made eyecatching progress to lead a furlong out and win tidily by two and three-quarter lengths.
Just The Judge put in her best work in the closing stages to finish third, with Ambivalent fourth.
“I’m really delighted. There’s not many things trainers get lucky at, but for a mare of that age to win a Group One and for it work out is hugely satisfying,” said Charlton.
“She travelled well and relaxed really well. She doesn’t mind whether it’s firm or heavy ground.
“She’s tough and she’s improving and it says a lot about keeping horses in training.
“She’s had a few problems, but she’s tough and sound and will be a great addition to the broodmare band.
“We were going to retire her after she finished second in a Group One (Nassau Stakes) last year, but the owner didn’t have any other horses with me and I thought she could win good prizes.
“We delayed putting her in foal and she’s done it now.
“It’s hard to say (where next), but courses like Goodwood suit and she could go for the Nassau again.
“We’ll pick and choose and take our time, there’s lots of nice races around Europe.”
Baker, who was riding with regular jockey James Doyle required for Noble Mission in France, said: “She travelled well and we got a lovely tow into the race.
“When she hit the front she was going through the motions, so it was a very good performance.”
Aidan O’Brien had to settle for second place with Venus De Milo in the main event, but he dominated the supporting card by saddling a four-timer with Gleneagles and Ernest Hemingway, both ridden by his son Joseph, and I Am Beautiful and Mekong River, partnered by Seamus Heffernan.
Ernest Hemingway (6-4 favourite) repeated last year’s victory in the Group Three At The Races Curragh Cup on his first start since Dubai in March.
The five-year-old was delivered with a sweeping run to lead at the furlong pole and win by two lengths from Certerach.
O’Brien said: “He loves fast ground, hard ground is the key to him. All his good form has been on that. He is able to quicken and put his toe out.
“He’s very ground dependent and he won’t go anywhere unless it’s good fast ground. We’ll look at the Goodwood Cup over two miles for him.”
Mekong River (5-1) put up a defiant display to win the Group Three Friarstown Stud International Stakes.
The three-year-old had tried to make all under Heffernan, but was headed by seasoned performer Parish Hall two furlongs out and looked set for second at best.
However, he battled back gamely on the far rail and gained the upper hand close home. Ebanoran, the 5-4 favourite was third but never got in a serious blow.
O’Brien said: “We weren’t sure about the fast ground for him, but on the good to firm ground he seemed to step up. He looks like a horse who will get a mile and a half.”
I Am Beautiful (12-1) was a surprise winner of the other Pattern race, the Grangecon Stud Stakes. Heffernan gave the daughter of Rip Van Winkle an enterprising ride as she just held the late thrusts of Jeanne Girl and Quinta Verde.
“I wouldn’t mind stepping her up in trip. We might take our time with her now she’s won her Group race and she’s very well bred,” said O’Brien.
Gleneagles got off the mark at the second attempt in the Barronstown Stud EBF Maiden as he went one better than his illustrious stable companion and dual Derby hero Australia, who was second on his racecourse bow in the same seven-furlong heat 12 months ago.
The evens favourite, a full-brother to Irish 1,000 Guineas winner Marvellous, benefited from a Leopardstown debut fourth with a promising display to score by two and a half lengths.
“I think he will get a mile but any further than that we don’t know yet. We’ll step him up to something like the (Group Three) Tyros Stakes (at Leopardstown),” said the trainer.
Gleneagles was given 33-1 quotes for the Qipco 2000 Guineas and Investec Derby with RaceBets.