State Of Rest held off odds-on favourite Bay Bridge to win the Prince of Wales's Stakes at Royal Ascot.
Shane Crosse dictated the pace perfectly on the 5-1 winner to give him and trainer Joseph O'Brien their first victory at the meeting.
The Irish challenger beat the Sir Michael Stoute-trained Bay Bridge by a length, with Grand Glory in third.
Previous winner Lord North was slow to start, while Japanese contender Shahryah finished fourth.
State of Rest was adding to top-level Group One wins in the USA, France and Australia.
O'Brien, 29, had won the Prince of Wales's Stakes himself as a jockey 10 years ago aboard So You Think, trained by his father Aidan, and praised Crosse's front-running tactics.
"It was a brilliant ride on a tough horse. It's very special to get a winner here," said the winning trainer.
"We love the game and were bred into the game and to have a big winner here is what we do it for."
It is another big-race success for O'Brien, who has also won the St Leger, Irish Derby, Irish Gold Cup and Melbourne Cup as a trainer.
Crosse had missed the ride on O'Brien's 2020 Leger winner Galileo Chrome, when replaced by Tom Marquand, because of a positive Covid test.
"This is an absolute dream - there's no other way to describe it," said Crosse.
Lord North, under Frankie Dettori, conceded ground at the start as the jockey struggled to remove the horse's blindfold when the stalls opened.
There was a dramatic finish to the Queen's Vase as 5-2 favourite Eldar Eldarov, trained by Roger Varian, got up in the dying strides under David Egan.
Eldar Eldarov, named after the MMA fighter by Bahrain owner Shaikh Khalid, won by the shortest possible distance of a nose from Zechariah, with Hafit in third.
"We've got the give the second credit, he ran a great race, we're all elated and he was on the wrong side of a tight photograph so I feel for the second," said Varian.
Kiwi jockey James McDonald, successful with Nature Strip on Tuesday, claimed a second winner of the meeting with Dark Shift in the Royal Hunt Cup.
The 13-2 chance triumphed for trainer Charlie Hills from Jane Chapple-Hyam's 40-1 outsider Intellogent.
Chapple-Hyam took the Duke of Cambridge Stakes with Saffron Beach, the 5-2 joint favourite, in the hands of William Buick.
French trainer Christopher Head's first Royal Ascot runner Sibila Spain was withdrawn after briefly ducking her head under the front of the stalls.
Saffron Beach, runner-up in last year's 1,000 Guineas, won by three and a half lengths from 40-1 shot Thunder Beauty, ridden by Danny Tudhope.
Tudhope had ridden a third consecutive winner at the meeting as 5-2 favourite Dramatised ran out an impressive winner of the the opening Queen Mary Stakes for trainer Karl Burke.
The rider, who had the last two winners on Tuesday, dropped his whip with more than a furlong still to go but it made little difference as his mount powered clear.
Following a nightmare start aboard King's Stand favourite Golden Pal on Tuesday, there was further woe for Irad Ortiz Jr, who was banned for five days for his ride on fourth-placed Love Reigns.
He was found guilty of careless riding after his mount drifted left-handed, causing Omniqueen to clip heels in the resulting congestion.
Aidan O'Brien landed his first winner of the 2022 meeting as 6-5 favourite Little Big Bear prevailed in the Windsor Castle Stakes.
Jockey Neil Callan celebrated his first Royal Ascot win since returning from a stint in Hong Kong, guiding Marco Botti's 40-1 outsider Rising Star to victory in the Kensington Palace Stakes.
Botti was the 14th different winning trainer from 14 races.
What to look out for on Thursday
Stradivarius, the mount of Frankie Dettori for trainers John and Thady Gosden, will go for a record-equalling fourth Gold Cup but must overcome Aidan O'Brien's highly rated Kyprios.
Dettori, the leading current Royal Ascot jockey with 76 career winners, is also set to ride stablemate Reach For the Moon, owned by the Queen. The horse is favourite to win the Hampton Court Stakes.
The Queen, who has yet to attend this year's meeting, also has Saga in the Britannia Stakes and Tactical in the Buckingham Palace Stakes.
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