A sister to Lloyd Williams' Group I Ranvet Stakes winner The United States, Hydrangea has played second fiddle to Ballydoyle stablemate Winter for most of the year, however, she turned the tables in the Group I Coolmore Fastnet Rock Matron Stakes at Leopardstown.
There was no excuse for Winter who was lining up for her fifth consecutive Group I win.
Previous to that she was beaten a head by Hydrangea in the 1,000 Guineas Trial back in April.
Rolly Polly took up the early running with Hydrangea and Wayne Lordan on her outside with Ryan Moore giving Winter the cosiest run behind the leader.
When Moore eased Winter out to make her run it looked as if it was a matter of how far for the grey daughter of Galileo, however, Hydrangea, also a daughter of Galileo, was up for the fight and she rallied to win by a head.
Persuasive three-quarters of a length back in third.
Cheveley Park Stud's Dark Angel mare Persuasive, who like Winter is out of a daughter of Choisir, was doing her best work at the finish to finish three-quarter of a length back in third.
Winning trainer Aidan O'Brien said it was a just reward for Hydrangea.
"I'm delighted for the filly and I'm delighted for Wayne," O'Brien told Irish Racing.com
"She is Winter's work partner all year, and maybe she turned around and said Hydrangea you can have this one today!
"She was the only one of the four fillies that had not won a Group 1. "We felt that Winter was going to improve a bit from the run. She was carrying a little bit of a tummy but needed to run.
"The winner will stay further. She could go for the Prix de
"Winter is in the Arc, and the Opera is another option."
Hydrangea is one of three stakes winners out of Pivotal's Group II Prix du Gros-Chene and Group III Prix
Besides Group I Ranvet Stakes winner The United States, who is now at stud in South Africa, Beauty Is Truth is the dam of the Group III Phoenix Sprint Stakes winner Fire Lily who was runner-up in the Group 1 Moyglare Stud Stakes and Group 1 Prix Marcel Boussac.
This the family of the former champion shuttle stallion Last Tycoon.
The Matron Stakes quinella was the appetiser for another highlight for Galileo as the day's feature, the Group 1 QIPCO Irish Champion Stakes fell to the 25/1 outsider Decorated Knight.
Winner of the Group 1 Tattersalls Gold Cup at the Curragh in May and runner-up in the Group 1 Prince Of Wales's Stakes at Ascot in June, Decorated Knight was off the board in Coral-Eclipse Stakes and Juddmonte International at his past two starts.
Ridden by Andrea Atzeni, the Roger Charlton-trained five-year-old powered home from the back of the field to defeat Poet's Word (Poet's Voice) by half a length with Sir Peter Vella's front-running Eminent (Frankel)
Favourite Churchill Downs was a troubled seventh.
Winning trainer Roger Charlton said the son of Galileo had genuine excuses for his last two failures.
"He's tough, consistent and very sound," Charlton told Irish Racing.com
He's produced an amazing turn of foot and ran right to the line. There was nothing flukey about it.
"He's been a bit unlucky in his last couple of races. He hated the ground at York, got bashed about at Sandown in the Eclipse and ran a great race at Royal Ascot.
"He's been on the go since March and he's improved and improved. To keep going all season is a tribute to the horse.
"I was half thinking that this might be his last race. I guess we will now look at the Champion Stakes at Ascot.
"Ireland has been very lucky for me with three Tattersalls Gold Cups, a Pretty Polly and now this."
Decorated Knight is the only winner out of the Storm Cat mare Pearling who is a sister to multiple Group 1 winner and Champion sire Giant's Causeway (USA).
Galileo's champion son Frankel got into the action at Leopardstown when his son Nelson led home a 1-2-3 for Aidan O'Brien the Group III Champions Juvenile Stakes.
Ridden by Donnacha O'Brien, Nelson kept up a relentless gallop to defeat two sons of Galileo, Kew Gardens and the favourite Delano Roosevelt by upwards of three lengths.
"He's improved with every run, and the experience was a big help," O'Brien told Irish Racing.com.
He got a nice easy lead and quickened up well off the bend. You would be delighted with all three of them really.
"He's very well bred by Frankel out of Moonstone and is a horse to really look forward to. He stays well and looks a Racing Post Trophy type horse.
Nelson becomes the fifth stakes winner for Group 1 Irish Oaks heroine Moonstone after Group III Chester Vase winner and G1 Epsom Derby runner-up US Army Ranger (Galileo), Group III Munster Oaks winner Words (Dansili) and the Listed winners Stubbs (Danehill Dancer and Nevis (Dansili).
But wait - the Galileo dominance continued at Leopardstown when his son Teofilo (IRE) sired the Group III Enterprise Stakes winner Eziyra.
The Aga Khan homebred made it four consecutive wins in the race for Dermot Weld and Pat Smullen.
Sent off an odds-on favourite, Eziyra defeated Exemplar by three-quarters of a length with Glamorous Approach a short-head back in third.
"She's tough genuine and game, Weld told Irish Racing.com
She's just a very good filly and ran a very good race in the Irish Oaks. Enable beat her fair and square but I think she's progressed and improved since then.
"She won the Group race in Cork nicely and you must remember she won over seven furlongs at Group level as a two-year-old as well. She's a stayer with speed.
"Interestingly Pat felt she would handle faster ground, good to
"I'd say she'll go for the Group 1 Fillies and Mares on Champions weekend. I won it a few years ago and this is a similar sort of filly. She'd be very capable of representing us very well.
"She'll also be in the Prix De Royaillieu on Arc weekend but I'd say we're more likely to go for the Group 1."
