Dartmouth made all of the running to provide for a Royal victory in the Boodles Diamond Ormonde Stakes at Chester.
The four-year-old colt had to give away weight to the rest of the field but was braveness personified in the hands of Ryan Moore.
Wilie Mullins' Wicklow Brave, whose jockey William Buick lost his whip close home, surged gamely towards the winning line on the far rail, but the Michael Stoute-trained Dartmouth had flown, with a neck the winning distance.
Moore said of the 11-10 favourite: "He's done well. We were really pleased with him and he enjoyed himself."
The Hardwicke Stakes at Royal Ascot could now be on the agenda for Dartmouth.
John Warren, the Queen's bloodstock and racing advisor, said: "He's a lovely horse.
"Sir Michael has typically trained him beautifully and now he has turned into a very useful older horse.
"He's an improver and a late-maturing horse and will give Her Majesty a lot of fun this year.
"Physically, he's starting to come to himself and now is probably the time to dip his toe into a slightly bigger pool.
"Her Majesty having a runner at the Royal meeting is always a thrill and we hope to get him there in one piece."
Willie Mullins said of runner-up Wicklow Brave: "The horse ran a cracker.
"I'm hoping he'll improve for that run and hoping he will improve throughout the season.
"I imagine we'd look at the Hardwicke at Royal Ascot. That would be our top target."