Azamour came from behind to claim the King George VI And Queen Elizabeth Diamond Stakes, breaking the track record at Newbury on Saturday. Stepping up to a mile and a half for the first time, Azamour - ridden by Mick Kinane - led over a furlong out.
The 5-2 favourite, owned by the Aga Khan and trained by John Oxx, beat 50-1 chance - and perennial Group One bridesmaid Norse Dancer by 1¼ lengths.
Bago was a further short head away in third, while Warrsan took fourth.
Last year's winner Doyen led briefly in the early stages of the race which was run at Newbury because Ascot is being redeveloped.
But he was headed by Gamut after a furlong with Ace and Mubtaker also close up.
However, Kinane was content to stay at the back and wait until the the straight before making his move.
Doyen took it up again three furlongs out, with Ace and Bago putting in their bids for glory
But ante-post favourite Azamour soon made up the ground, edging past the leaders a furlong and a half out on the outside.
Despite Norse Dancer and Bago challenging strongly in the closing stages, the colt held on to win in a time of two minutes, 28.26 seconds - 0.945 seconds faster than the previous course record.
"I have a lot of confidence in the horse and he repaid it in style," said Kinane.
"He is a very very high class horse but I wouldn't like to compare him to others I have ridden as I am focussed on the present."
"In the Irish Guineas the feeling was that he was taken a little bit by surprise. We thought that he was a very useful horse and the rising ground here was what we were looking for," said winning owner the Aga Khan