Shane Crosse left Bay Bridge backers cross by making all the running on 5/1 shot State Of Rest, burning off the favourite and Japanese raider Shahryar in the Prince Of Wales's Stakes.
Joseph Patrick O'Brien's four-year-old was mentioned only in dispatches in the build up but made a mockery of the odds by leading from start to finish in a true speed horse performance.
Both Sir Michael Stoute's six-timer chasing Bay Bridge and Hideaki Fujiwara's Dubai Sheema Classic winning Shahryar were well placed behind O'Brien's Starspangledbanner colt but just couldn't respond when the son of a sprinter kicked for home
The race started in dramatic fashion with Frankie Dettori unable to remove the hood of the winner from two years ago, Lord North and the five runner field just couldnt budge State Of Rest from the front.
It was young Joseph O'Brien's first Ascot winner and a tactical plan to lead from the front that his father Aidan would have been proud of.
Ryan Moore tried to level the deficit on Bay Bridge for Stoute, who first won the race in 1981 but Crosse wasn't for moving and passed the line a length in front for a memorable win which truly starts a new O'Brien dynasty.
Gianluca Bietolini's French raider Grand Glory did well to finish third, a further two and a quarter lengths back under Mickael Barzalona with Japanese athlete Shahryar not coming on from his Dubai Sheema Classic win.
Victorious young jockey Crosse said: "The plan beforehand in a small field was to uncomplicate things from our draw.
"Fair play to State Of Rest. He has done it all and I am just over the moon.
"In the space of the last 12 months, this horse has done a lot. I am over the moon.
"It is a dream. To get here and participate is a huge thing. To ride a horse like this in top-class races is a dream. You cannot describe it."