The Americans had never seen anything quite like it when the Irishman's gravity-defying millinery creations took to the runway for the first time at New York Fashion Week on Tuesday night. They whooped, they clapped, they gasped. They nearly cried as an organdy shell-hat followed silken fossils, lily leaves, perspex sun visors, and a stiff organza scarf with fairy lights twinkling inside it down the catwalk, balanced perfectly on the heads of Treacy's favourite models, Honor Fraser, Stella Tennant, Michele Paradise and Naomi Campbell.
Treacy was given a standing ovation. No one in hard-faced New York rouses the jaded old fashion pack to their feet. Ever.
This week, the hat magician has New York at his feet. He is something that the Americans can't quite put their finger on - "simply genius", as they would say, but not a cigar-toting, besuited corporate man. He is about as interested in business figures as Tommy Hilfiger is in setting a new trend in asymmetric skirts.
For his stay in New York, Treacy has been given a car from his sponsor, Rolls-Royce, and a driver to run him from party to cocktail to meeting. In the city where limos the length of small trains are 20 a penny, a roller still makes heads turn. But there are bemused looks when Treacy steps out of the car with his unkempt hair, unshaven face and free Virgin Atlantic sweatshirt.
When his show started late, a member of the American press was overheard saying, "Oh, he's European. He doesn't have to start on time." He can do what he pleases, as he pleases, as long as the hats are sublime.
Of course, not one person in the audience was wearing so much as a tiny little pill-box, not to mention a practical beret. Hats designed for neither keeping your hair dry nor your ears warm are so frivolous that even the fashion pack don't wear them.
Isabella Blow, Treacy's friend and a rare breed of hat wearer, who has been known to sit all the way through dinner with an impenetrable lace veil pulled down over her face, was not in New York for the show. She's not the type to pick up a duster or a Hoover to clean the house, but if ever she did, she would choose a hat for the occasion.
The art of hat-wearing has almost died out. In the Forties, a woman would feel naked without a hat to match her outfit. Today, it takes a wedding or a day at Ascot for most women to pin a hat to their heads. Even then, the chances are that it would be something plain, old and straw. Yet Treacy's hat couture collection was the most feted show in New York this week. His one-off catwalk creations, which take up to 60 hours' work apiece and cost upwards of pounds 400, will be photographed by fashion magazines the world over and lusted over with gusto. But sadly, few will actually take the plunge and buy one.