Diamondsandrubies denied Legatissimo in a driving finish to the Sea The Stars Pretty Polly Stakes at the Curragh.
The Aidan O'Brien-trained filly made all under Seamie Heffernan and just held the challenge of the Qipco 1000 Guineas winner to claim the Group One spoils.
Diamondsandrubies (8-1) was reversing Investec Oaks form with Legatissimo, having finished two places behind that filly at Epsom when fourth to Qualify.
There was just a short head between the pair, with the James Fanshawe-trained Ribbons close behind in third under Frankie Dettori.
Heffernan said: "I rode her in Epsom and it didn't really swing my way. Sometimes Epsom finishes a horse and sometimes the good horses thrive on it. She's obviously good.
"We thought she'd stay and I jumped and she landed in front and I was happy enough to go along with it. I knew they (the challengers) were coming. I knew where the line was.
"I was a bit unlucky at Epsom. Aidan trains them to progress from run to run and today she was at her best, so hopefully there will be more improvement."
Diamondsandrubies, who had also impressed when winning the Cheshire Oaks, will now go for the Darley Irish Oaks on 18 July.
O'Brien said of his filly, who had been badly hampered a furlong and a half out at Epsom: "She was very unlucky at Epsom and was probably the most inconvenienced by the whole thing. She was always going to come here and we said we'd let Qualify take her chance in the Derby.
"We'd like to have got a lead but that's not the way it worked out, and Seamie gave her a great ride. Emmet McNamara rides her out every day at home and does a great job.
"We know the dam well and I'm delighted for Richard and Roisin (Henry, part-owners with Sue Magnier).
"We'll ride her a bit more patiently over a mile and a half, and Qualify and Words will also run in the Irish Oaks."
Sanus Per Aquam got the better of Lieutenant General in a terrific tussle for the Barronstown Stud EBF (Colts & Geldings) Maiden.
Donnacha O'Brien looked like he had made a winning move on the newcomer, trained by his father Aidan, but Kevin Manning plugged away on Jim Bolger's fellow debutant Sanus Per Aquam (7-1).
The son of Teofilo asserted close home to win by a length and a quarter. Leath Na Hoibre was third.
"He's a big raw two-year-old and has the physique to progress well," said Bolger of the winner who is a full-brother to the year-older Morning Mix, who was successful at the meeting on Friday.
"He could come back here for the Futurity and possibly the National Stakes after that.
"If I was a proper trainer you wouldn't see him next until a Derby trial!"
The race was won last year by subsequent dual Guineas hero Gleneagles.
BoyleSports introduced Sanus Per Aquam at 33-1 for the Investec Derby, while RaceBets offered an introductory quote of 25-1 for the Qipco 2000 Guineas.
Ryan Moore made all the running on Air Pilot as the Ralph Beckett-trained six-year-old landed his first Group Three success in the Hermitage Medical Clinic International Stakes.
Air Pilot (8-15 favourite) enjoyed an easy lead and had enough in the tank to comfortably see off the attentions of Parish Hall, representing the opening-race winning team of Bolger and Manning.
Roheryn was some way behind as last of the three runners.
Beckett said: "We were lucky to fall into a three-runner Group Three. There's not many of those around and we didn't want to make the running as he's lazy in front.
"Ryan felt he probably did more on Thursday morning before he came over. I thought Ger Lyons' filly (Roheryn) was sure to go on, but they obviously decided otherwise.
"He's a home bred and had problems as a three-year-old and only came to me at the beginning of last year. He's ground dependent and needs juice in the ground. The rain last night was a big help. He was entitled to win a race of that nature."
Have A Nice Day (8-1) ran out a determined winner of the Sunday Independent Handicap.
Sabrina Harty's five-year-old was handy throughout in the hands of Leigh Roche and had enough in the tank from the furlong marker to repel the challenge of Hunt and Andrea Atzeni by half a length.
Harty said: "He won this race last year but was 12lb higher today. He's a little legend and is the most consistent horse in training. He was quite keen and fresh but is so laid-back at home on the gallops. He loves the Curragh.
"He ran great at Galway last year in a Premier Handicap behind three English horses. I'd love to have a yard full of ones like him."
Most Beautiful confirmed her promise with victory in the six-furlong Grangecon Stud Stakes.
Given a positive ride from Moore, the David Wachman-trained filly tracked the unbeaten Miss Elizabeth to the quarter-mile pole, before hitting the front with a furlong to run.
Moore had to keep her up to her work as Only Mine tried to challenge on her outside, but the well-backed 11-8 favourite kept on strongly to record victory by three-quarters of a length.
Wachman said: "She's always worked like a good filly. She's big and is still a bit weak, you could see that in the last furlong. She has a nice future.
"Ronan (O'Gara, part-owner) couldn't be here today as he's on a family holiday in the south of France, but I'd say he won't miss the next day wherever that is.
"She's well entered up and will go further. The one thing is she likes goodish ground."
RaceBets make the daughter of Canford Cliffs 20-1 from 25-1 for the Qipco 1000 Guineas.
Foxy Forever (20-1) proved reluctant to go into the stalls but was a most willing parner in the race itself as Michael Wigham's sprinter blitzed the opposition in the Tote Rockingham Handicap.
The five-year-old, blinkered for the first time, delayed the start slightly and jockey Colm O'Donoghue even dismounted briefly as the horse was led round from the front of the stalls before he jumped back in the saddle.
Last into the gate, Foxy Forever got a flier from his stands side draw and never saw a rival as he scooted up to land this valuable prize.
The winning margin was two and a quarter lengths from the Mike Murphy-trained 6-1 favourite Discussiontofollow with Paul Midgley's Desert Law third as British raiders took the first three places.
