Declaration Of War swept to victory for the Aidan O'Brien team in the opening Queen Anne Stakes at Royal Ascot.
Joseph O'Brien had trouble finding a gap heading into the closing stages, but once in the clear the four-year-old stamped his class on the Group One race and surged to an emphatic victory.
Hot favourite Animal Kingdom, the Dubai World Cup winner, was a major disappointment as he pulled hard and was one of the first horses beaten, weakening quickly to finish in arrears.
Declaration Of War, always held in high regard by the Ballydoyle team, was a 15-2 chance to bounce back from a disappointing run when favourite for the Lockinge Stakes at Newbury last month and was always travelling strongly before sweeping through to beat Aljamaaheer by three-quarters of a length, with Gregorian third.
The winning rider said: "I'm not really quite sure what happened in the Lockinge. Dad thought he wasn't quite as fit as he'd hoped to have him. He said he had him 100% today and he was bang on.
"I was going very well and I just went into the gap. It got a little bit tight, but he was going exceptionally well and quickened up well, but he idled when he got there. He's a very good horse. We thought that at Newbury and we were a little bit disappointed, but we sorted a few things - all the lads in the yard have done a great job. It's nice to start off on the front foot."
O'Brien senior added: "We are delighted. We thought the world of him last year. He just had an easy win first time at Leopardstown and then he went to the Lockinge. I left him unready and he wasn't ready for the race at the time, but he has made great progress since and has come back to what we thought and hoped he would be.
"He has a lot of speed, so Joseph waited as long as he could. He's a big, powerful horse and when he asked him he put his head down and went through."