Having tracked the early leader, Scottish, he was sent to the front at the top of the straight and had to resist stern challenges from Decorated Knight and Ulysses, who both edged past him inside the final furlong.
O'Brien was effusive in his praise of the victor.
Asked about plans, O'Brien said: "He'll come back here for the King George, that's what we were thinking if he ran well today".
"I hope now that she will continue to improve for the rest of the season". "With that in mind, I do think that this filly is a big filly and I feel that she will mature into something special in the future".
"There's been no formal meetings at this point but I did make sure I sent them a text after the win last night to say congratulations and remind them of my interest for the Everest", Flower said.
Qemah had been beaten on her last start at Lingfield, but she put that behind her back at Ascot with an impressive performance.
Michael Bell's Big Orange will be ridden by James Doyle in the absence of Frankie Dettori, but his trainer admits the trip is a bit of an unknown for the dual Goodwood Cup victor.
The 4.20pm is the day's feature race and runs over two miles and four furlongs, considerably longer than any of the other races on the day.
"You've got to hand it to the horse, he's an absolute jockey's dream". "She settled well the early part, which I expected". He's not stamped his authority on the race yet.
"He'll run his race". Lady Aurelia is a very special filly. A big credit and well done must go to everybody at home that is involved with him.
Simple Verse won the 2015 St Leger for Ralph Beckett and made a pleasing return to action in the Yorkshire Cup.
The nine-year-old seemed to be engrossed in the racing action, receiving a celebratory hug from her dad as their horse stormed to victory. Throw in the likes of the Argentinian recruit Greta G and this is a very lively heat.
Al Jalila seemed engrossed in the racing action, enjoying a sweet celebratory hug from her father at one point during the day.
"It was good pressure to have, he was not odds-on in the end and he was the right horse to have the pressure with as sometimes you get favourites that can't win". A mile and a quarter here in the autumn on soft, no problem - but this isn't his ground.