Already favourite for next year’s Derby, Anthony Van Dyck had won the Tyros Stakes last time out.
While he always looked to be in command, Ryan Moore was eventually made to work harder than might have been expected for a 4-6 favourite, but still crossed the line with half a length to spare from Christmas.
O’Brien said: “I’m delighted. They needed to learn a little bit and that’s why they swung along there. You’d have to be very happy.
“The last day was his first time back to seven (furlongs). He gets a little bit lazy in the middle of the race, but gets there, and he was doing it well again in the last furlong.
“I would imagine that they’ll all probably come back here for the National Stakes. I’d say he’ll get a mile well, we always viewed him as a horse that would get middle distances next season.
“He had a tough enough race as they went all the way.”
Earlier, Skitter Scatter ran out an impressive winner of the Debutante Stakes at the Curragh for trainer Pat Prendergast.
Lining up as the most experienced filly in the field, she was having her sixth outing and was sent off at 7-1.
She had won two of those, including the Silver Flash Stakes last time out, but this looked an improved performance.
Ronan Whelan always looked to have everything covered and when the expected challenge from Zagitova failed to materialise Skitter Scatter scooted clear.
Jim Bolger’s 50-1 chance Bandiuc Eile stuck on for second with Zagitova only third.
“I’m delighted. I was very worried about the rain but she’s so honest,” said Prendergast.
“She deserves her place in the Moyglare as she has kept improving all year. If the Moyglare turned out to be heavy we’d worry some more but at the moment that’s where we are going.
“Hopefully that and then we’ll go for a Guineas trial next year.
“She’s all guts and she makes training very easy because she’s very very honest and sound. The main thing is that she actually tries to do too much.
“My staff have done a marvellous job with her. I’m so grateful that a small yard like ours has something like her.
“I love to buy and sell them but it can be frustrating too. It’s lovely to have one like that and we know we’re keeping her.”
Beautiful Morning returned from a mid-season break to win the Manguard Plus Royal Whip Stakes in thrilling fashion.
It looked for all the world that Deauville had held off Jessica Harrington’s mare as the pair flashed across the line together.
But Beautiful Morning (5-1), having her first run since May, relished the rain-softened ground and held a nose advantage at the line.
Jim Bolger’s Group One winner Verbal Dexterity was returning from a 302-day lay-off and finished close up in fourth.
“I was very happy to see the rain,” said Harrington. “She was very keen until the four-furlong marker and he had to sit and wait on her and then go for her.
“She’s getting there. It’s a long time since she’s run and it’s been a bit of a frustrating summer with her.
“She’ll probably run in the Blandford because the owner is coming that weekend (Champions Weekend). She’s won a Group Three now anyway.”