Deirdre came from way off the pace to win the Qatar Nassau Stakes at Goodwood and record a historic success for Japanese trainer Mitsuru Hashida.
Settled way off the pace by Oisin Murphy as Mehdaayih and Hermosa set a stiff gallop, the five-year-old stayed on powerfully to notch a famous overseas win.
Brought over to run at Royal Ascot, the Harbinger mare was undone by soft ground in the Prince of Wales's Stakes and her connections took the brave decision to keep her in Britain for a while longer.
Although an unconsidered 20-1 chance, Deirdre had form against some of the best horses in the world, such as Almond Eye and Glorious Forever, and eventually ran out a clear-cut winner.
Ryan Moore was the first to send out distress signals on Aidan O'Brien's dual Guineas winner Hermosa, who dropped away with three furlongs to run.
But at that stage Frankie Dettori appeared to have stolen a march on the John Gosden-trained Mehdaayih, who looked set to provide the red-hot trainer and jockey combination with another Group One triumph.
Deep inside the final furlong, though, Dettori's mount had no answer to Deirdre, who won going away by a length and a quarter.

Student Khadijah Mellah registered a fairytale victory as she steered Haverland to victory in the Magnolia Cup at Goodwood.
The 18-year-old was the first rider to race in a hijab in Britain and she delivered her Charlie Fellowes-trained mount with a perfectly-timed run to lift the ladies-only charity race.
Mellah, who hails from Peckham in South London and is set to study mechanical engineering at university in September, learnt to ride at the Ebony Horse Club charity in Brixton - but sat on a racehorse for the first time only in April.
She certainly belied her lack of experience, as she exercised plenty of patience aboard Haverland, only making her move coming into the final furlong.
It was a blanket finish to the race, but after a tense wait, Haverland was eventually called the winner by the judge.
Irish reality TV star and presenter Vogue Williams was sixth on The Magic Sign.
Charlie Hills will seek to clinch Pattern-race glory with Vividly on her next start following her victory in the Markel Insurance British EBF Maiden Fillies' Stakes at Goodwood.
Having finished third on debut at Newbury last month, the daughter of Charm Spirit boxed on tenaciously to hold off Craylands by a short head in the seven-furlong contest, which was won in 2016 by subsequent Group One scorer Rhododendron.
A return to the Sussex track looks to be on the agenda for the Khalid Abdullah-owned filly, with the Lambourn handler hinting at an outing in next month's Group Three Ladbrokes Prestige Stakes.
Owner Rob Ferguson was out of luck with Visinari in the Vintage Stakes on Tuesday, but he enjoyed a winner before heading back to Australia after Governor Of Punjab completed a hat-trick in the Telegraph Nursery Handicap.
Tom Clover celebrated his first ever winner at the meeting after Celsius (11-2) made it four wins from five starts this season with a short-head verdict in the Tatler Handicap.
The Newmarket handler said: "It's terrific. Gelding this horse has helped him, as has the tongue tie, and the lad who rides him at home as helped a huge amount.
"When he was rated 58 I told the owners he was a nice horse and they looked at me a bit sideways. He has proven he is a nice horse now. They preserved with me and the horse and I'm so glad it has paid off."
Nayef Road will be aimed at the William Hill St Leger following his gutsy success in the Qatar Gordon Stakes at Goodwood.
Technician briefly flattered on the outside, as did Floating Artist, but it was Nayef Road (9-1) and Silvestre de Sousa who saw off Constantinople by a neck, with Spanish Mission not far behind in third.
After a record 50 winners in July, Middleham trainer Mark Johnston was beginning August with a Group Three winner and the victory saw him edge in front of Michael Stoute as the winning-most trainer at Glorious Goodwood on the 81-winner mark.