The Derby winner Erhaab was Ezzoud's first target, then he took out Foyer, King's Theatre and Wagon Master, who in turn clattered into Bob's Return. Ezzoud, riderless and blinkered, veered this way and that before giving up the contest, and passed the post first with his ears pricked.
The five-year-old was fractious in the parade, and was unsettled in the stalls, leaning against the superstructure. He lurched left and cannoned into the gates as they opened, catapulting Swinburn from the saddle. The jockey was taken to a local hospital, where X-rays revealed no broken bones. Swinburn hopes to be back in the saddle at Goodwood.
Bob's Return, and then the handicapper Urgent Request, set a good gallop, and a buzz went up from the packed grandstand as the loose horse was spotted running free.
Approaching the straight the others were queuing to take the leaders, with Ezzoud running wide, but on the run for home the herd instinct took over and the riderless one joined his fellows with devastating effect.
Willie Carson, on Erhaab, gave up the chase once his little partner was out of the game and came home seventh. But King's Theatre disentangled himself and, with the big-race specialist Michael Kinane riding another superbly competent race, hit the front a furlong out and had more than enough in reserve as White Muzzle came out of the pack after him.
King's Theatre, a doughty colt, gained ample reward after his second places in two Derbies - to Erhaab at Epsom and Balanchine at the Curragh - and silenced those who doubted his ability to win over a mile and a half at the highest level. Kinane said: 'He had the pace to keep to the front of the pack, and he's tough and hardy. I had some trouble getting through when the loose horse came across, but King's Theatre has absolutely the right attitude for that sort of situation.'
King's Theatre, winning at Group 1 level for the second time - he took the Racing Post Trophy as a two-year-old - looked better in the preliminaries than he had done all season.
It was touch and go whether he ran - he does not function best on fast ground - and his trainer Henry Cecil, winning the glittering prize for the third time, praised the Ascot authorities for their watering of the ground during the prevailing dry weather.
He said: 'They got it perfect, just enough to take the jar out of it. He likes to get his toe in; in Ireland it was too yielding and he was always struggling against a very good filly.'
King's Theatre carried the colours of Sheikh Mohammed, who owns the Sadler's Wells colt in partnership with his breeder Michael Poland.
White Muzzle was a worthy runner-up, for the second year in succession, and shares favouritism with King's Theatre for the Prix de L'Arc de Triomphe at Longchamp in October, at 8-1 with Hills.
The four-year-old's trainer Peter Chapple-Hyam had nothing but praise for the jockey Yukata Take, about whom doubts had been expressed in some quarters beforehand. The Japanese champion had to take a slight pull in the scrimmage, but the winner suffered more.
Wagon Master ran on well to take third place, followed by Apple Tree - not suited by the undulations of the course or its right-handed direction, according to his trainer Andre Fabre - Petit Loup, Foyer and Bob's Return.
Remembering the way he brushed aside King's Theatre at Epsom, seventh place represents a dismal performance for Erhaab. 'He did not run his race. He was interfered with but that's not the reason he got beat,' said Carson. And trainer John Dunlop reported: 'Erhaab is not 100 per cent as he is not using himself. There is still something niggling him. He will now have a break as there is nothing for him.'
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