The Coolmore team had suffered a host of near-misses earlier in the week – with Age Of Aquarius’ late mugging by Rite Of Passage in the Gold Cup on Thursday a prime example.
But Lillie Langtry resumed normal service and provided O’Brien with his 29th Royal Ascot winner as she forged clear under Johnny Murtagh as the 7-2 favourite.
The English and Irish 1000 Guineas have served up mixed messages in terms of form, but with only Special Duty of the key contenders absent Lillie Langtry proved herself superior.
Gile Na Greine had finished a close third in the English Classic and flopped in the Irish equivalent, but almost caused a mighty upset with Jim Bolger’s 25-1 outsider kicking for home over two furlongs out.
Murtagh did not hit the panic button in behind, though, and angled his filly out to challenge at the two pole.
She responded willingly and soon drew upsides before going away to assert by a length and a quarter to become just O’Brien’s second winner of the race after Sophisticat eight years earlier.
The daughter of Danehill Dancer picked up an injury at the Breeders’ Cup last autumn but hinted at a fruitful season ahead when staying on for fifth on her seasonal bow in the Irish Guineas.
O’Brien said: “It is a relief as everyone puts a lot of work in and it is a privilege to be part of the team.
“The horses have been slow to come to hand and it has been tough so it is great it has happened today.
“We have been trying to peddle as fast as we can without the chain coming off.
“The lads haven’t put any pressure on but you feel it for everyone.
“It is a credit to everyone involved to get her back from the injury she sustained in America.
“She was just ready to start at the Curragh and she came home well.
“Johnny was looking forward to riding her and she quickened up really well.
“You dream of these things but they don’t always happen.
“She has the option to step up to a mile and a quarter in either the Pretty Polly (at the Curragh) or the fillies’ race (Nassau) at Goodwood.
“We’ll have to decide whether she stays at a mile or steps up to a mile and a quarter.”
Murtagh added: “You can get carried away at Ballydoyle riding Group One winner after Group One winner so it has been a bit testing, but you can’t be feeling sorry for yourself.
“A friend rang me last night and said he thought the Gold Cup was a great race, but I didn’t think so passing the winning post.
“I have had a few seconds and you need a bit of luck – I have got it today.
“She’s a champion and I thought she was by far our best filly last year - going to America I was telling Aidan how far we were going to win the Breeders’ Cup by.
“She has speed, heart and a great temperament and Aidan has nursed her along.
“It was an encouraging run in the Irish Guineas and if I had been more aggressive on her she may have won.
“I thought she was one of my better rides of the week and I think it rode like a pretty strong Coronation.”
Bolger saddled Lush Lashes to take the Coronation two years ago and almost repeated the feat with Gile Na Greine.
He said: “I’m pleased. We drew a line through her run at the Curragh – she’s a good filly.
“We’ll take her home now and see where we are. She carries plenty of condition and she behaves a bit like a colt in that we can get plenty of mileage out of her. She won’t be going back in trip, that’s for sure.”
Jacqueline Quest was heart-breakingly demoted from first place in favour of Special Duty in the 1000 Guineas at Newmarket.
A 66-1 chance that day, she proved the run no flash in the pan as she finished a little over two lengths adrift in third.
Trainer Henry Cecil commented: “Jacqueline Quest ran very well – there are no excuses – and those fillies are the best there are. I haven’t got a plan for her at the moment.”