So You Think (4-5 favourite), now a 10-time Group One winner, was pipped by Rewilding in a thrilling race 12 months ago and had proved able enough to take an Eclipse and an Irish Champion Stakes without quite living up to the legendary status accorded by Australians for his formative period with Bart Cummings.

O'Brien revealed he had jettisoned his previous training regime, moving towards the principles from Down Under, but he may have only one more race to enjoy him as the son of High Chaparral is to return to Australia for stallion duties later this summer.

The trainer's son, Joseph, who continues to show thought and craft far beyond his 19 years, stuck close to his pacemaker Robin Hood and evaded the cannily-ridden Carlton House to surge two and a quarter lengths clear by the line.

"I think we've had him a year and a half and it's taken me that long to learn how to train him," said O'Brien Snr.

"We were working him too long, too hard and too often. It was as simple as that.

"We went back and listened to what everybody was saying about him, listened to what Bart was saying and telling us what to do and what not to do. We listened at the end.

"We felt he was in a place today he's never been in before.

"In Australia it's all about speed, I was probably over-working the horse and galloping the speed out of him instead of letting him be natural.

"We're just delighted to get him back and all I can say is sorry it took me so long to get him back to where everyone in Australia said he was. If he wasn't such a great horse I'd have made a right mess of him."

O'Brien strongly suggested the Coral-Eclipse at Sandown on July 7 will still be on the agenda.

"I think the cut-off point for going back to Australia is after Sandown - I hope it is," he said.

"The boys will discuss it. We'll be pleading hard now that we have him in this place but it's a business decision.

"If he runs, then that's great, but if he never runs here again at least he has shown how good he is."

Winning rider O'Brien jnr said: "Ryan (Moore, on Carlton House) got a split on the inside and I just had to come around Johnny (Murtagh, on Big Blue Kitten) but once he could see the horse on his inside he was never going to get beat.

"I just wanted to get him into a rhythm and get him relaxed, he has loads of class and can quicken and when things work out he's an exceptional horse."

O'Brien was riding his first Royal Ascot winner, hot on the heels of his first Derby through Camelot.

"It's been a great season and I'm very lucky to get to ride some exceptional horses," he said.

"I owe a big thanks to Mr and Mrs Magnier, Mr and Mrs Tabor and Mr and Mrs Smith for giving me some nice opportunities."

Trainer Michael Stoute was sporting about defeat for last year's Derby third Carlton House and said: "He couldn't get enough cover as he was a bit off the fence but he was second best, it's as simple as that.

"Ryan gave him a great ride, he had every chance but he just found one too good. We need to stop really and see how he comes out of the race but he doesn't want to be going any further than this."

The lightly-raced Farhh was taking a big step up in class but enjoyed very little luck during the race as he flashed home for third.

Trainer Saeed bin Suroor could aim him for the Eclipse or the King George, with Alain de Royer-Dupre's Reliable Man pencilled in for the Juddmonte International after a respectable fourth-placed finish.