Having his first race since winning the Coral-Eclipse Stakes at Sandown 10 weeks ago, St Mark's Basilica (5/6 favourite) showed his trademark brilliance to overcome two Group One winners in Tarnawa and Poetic Flare in an absorbing tactical affair for the mile-and-a-quarter showpiece.
Aidan O'Brien's crack three-year-old colt had missed the Juddmonte International at York due to a setback - but was able to show his superiority to add this race to his victories in the French 2000 Guineas and French Derby this season.
Patrick Sarsfield, the outsider of four, made the running until inside the final quarter-mile where the other three knuckled down to battle it out.
St Mark's Basilica drifted right in the closing stages, taking Tarnawa with him, but got the verdict by a three-quarters of a length in the hands of Ryan Moore - although it was anxious wait for the result to be confirmed in a stewards' inquiry.
Poetic Flare was a nose away in third place, on his first start over 10 furlongs. Patrick Sarsfield was seven and a half lengths away last of the quartet.
"It was great because it was very tactical," said O'Brien.
"They sprinted up the straight and he did well. He had a bit of catch up to do after the last day (missing York).
"One thing we knew is that he does quicken. That's what he always had - his strong qualities are that he relaxes and can really turn it on.
"They set off a nice pace, Kevin (Manning, on Poetic Flare) was in second and he steadied it down to get himself straightened up and set up.
"When they turned in they burned and I'd love to see what time they did for the last two furlongs. They ran up the straight.
"He's just an exceptional horse and we're very lucky to have him. All the lads at home have done a great job with him to get him back here today after the last day."
He added: "The two targets he had were York and here, and after that we were going to see what way he came out of it and see what way we were going to go.
"He has all the options, he can go back to a mile or go a mile-and-a-quarter. All those races have to be there. A little bit of a problem with the QEII, we know that he handles soft ground but Ascot can be run in very bad ground.
"He did well to get back here after York and we'll see how he is after this."