Chipotle won the Listed Windsor Castle Stakes for Charles Bishop and Eve Johnson Houghton.
Starting at 22-1, the Brocklesby winner travelled at the rear of the group on the far side of the track, striking late to pick off his rivals.
Dig Two was second at 7-1, with Boonie coming third at 18-1, but it was another disappointing race for American trainer Wesley Ward with his Frankie Dettori-ridden favourite Ruthin ultimately well beaten having led for a long way.
"A lot of credit to the trainer, I'd say," Bishop said.
"I've only had two winners here and they've both been hers, she's unbelievable.
"We were very disappointed at Sandown, we thought he was very good and the ground just completely blunted his turn of foot.
"No excuses today, he showed he was the best horse in the race.
"It's not very often you get a run like that at the Royal meeting, I had the horse to go for the gaps.
"They weren't very big, he was very brave."