Jockey Frankie Dettori rode Stradivarius to a 10th successive victory in the Doncaster Cup.
The five-year-old finished one-and-three-quarter lengths clear of Cleonte, with Max Dynamite third.
Stradivarius trailed Andrew Balding-trained Cleonte entering the home straight, but Dettori reeled in the leader for a comfortable victory.
"That's the easiest he's won - he's so great to ride, he relaxes, he quickens. Brilliant," said Dettori.
"It was a messy race, but we expected it to be like that."
Stradivarius was not expected to race again until the Long Distance Cup at Ascot next month, but trainer John Gosden said he was too fresh.
"I had no intention of coming here," said Gosden. "But he was so fresh, rearing up and shouting all the time, so I thought we'd come and win the Doncaster Cup."
Stradivarius has dominated the staying division over the past couple of seasons, with back-to-back wins in the Yorkshire Cup, Gold Cup, Goodwood Cup and Lonsdale Cup.
Gosden says owner Bjorn Nielsen will now target a third successive Gold Cup at Ascot next June.
"I think Mr Nielsen's big plan, if the horse is happy and well, is to go to Ascot next year," he said.
"He would love to win three Gold Cups. We'll try to do that if we can."
'The Arc will probably be the plan' - analysis
BBC horse racing correspondent Cornelius Lysaght
No Dee Ex Bee was a big pity, but in this majestic form it's hard to imagine he'd have laid a glove on Stradivarius, who breezed home from the gallant Cleonte.
Stradivarius' appearance here was a surprise - conventional wisdom was that he'd go straight to Champions Day at Ascot - but John Gosden explained he was "so playful" after an easier year than 2018, that a race was something of a necessity.
If the big ambition of a third Gold Cup win at Ascot is achieved in June 2020, the Arc will probably be the plan this time next year