So You Think beat Workforce in a thrilling finish to the Coral-Eclipse at Sandown.
The Australian import, bred in New Zealand and now trained in Ireland by Aidan O'Brien, reeled in the long-time leader in the final furlong.
Workforce, the 2010 Epsom Derby and Prix de l'Arc de Triomphe winner, had gone into the lead in the home straight.
But Seamie Heffernan bided his time and the 4-6 favourite won by half a length.
Workforce came into the race on the back of a seasonal comeback win at Sandown, while dual Cox Plate winner So You Think suffered a shock defeat to Rewilding at Royal Ascot.
Stablemate Confront set the early pace for the Sir Michael Stoute-trained Workforce, but jockey Ryan Moore sent the Derby winner to the front with about half a mile to go.
It looked as though Workforce's stamina may come into play, but So You Think demonstrated why he has excited punters in two hemispheres as he found the speed to overtake the second favourite and claim a seventh Group One triumph after a pulsating duel.
Last year's runner-up Sri Putra put up another fine effort in defeat, finishing third, but dual Oaks winner Snow Fairy was fourth of the five runners.
O'Brien, who said he had under-worked his horse before Ascot, was delighted with the victory.
"He was where we hoped to have him in Ascot, but those things don't always work out. He's a smart horse and Ascot left him right for today," said the trainer.
"Seamie followed Ryan and the race started three [furlongs] down. Seamie just sat away, angled him out and he's won nicely. He gave him a lovely ride.
"He's got a lot of options now, he could go back to Australia for something like the Cox Plate [which he has won twice], but we are trying to get the quarantine sorted and it's not that simple.
"Otherwise, there is the Irish Champion Stakes and the Juddmonte International."
He said the horse, who was third in the Melbourne Cup in November, could potentially run over further than 10 furlongs later in the season.
"As long as he settles, with the speed that he has, the sky is always going to be the limit," said O'Brien.
Despite neither race being immediately mentioned as a target, bookmakers William Hill cut So You Think to 9-4 from 4s for the King George at Ascot later in July, while he is 4-1 (from 7s) for the Arc at Longchamp in October.
Stoute indicated he would aim Workforce at a second Arc win.
"The winner's a very good horse and ours is a very good horse. You have to be pleased with that, as his best form is over a mile and a half," he said.