Fairyland just denied The Mackem Bullet on the line in a thrilling finish to the Sky Bet Lowther Stakes at York.
The pair fought out a terrific duel in the final furlong with Brian Ellison's 25-1 outsider The Mackem Bullet looking as though she might just win the battle.
However, Fairyland (6-4 favourite), who had been up front throughout battled on bravely for Ryan Moore and got the verdict by a nose. Queen Jo Jo was two lengths away in third place.
The disappointment of the Group Two heat was Angel's Hideaway, who faded out of contention after being short of room when the race hotted up in the final quarter-mile.
O'Brien said: "We were very happy with her at Ascot (third in Albany Stakes), but she was under the weather in between. I'm delighted with her. She did get headed so it was great to see her battle back. Ryan said she had a blow two (furlongs) out, which was understandable. She's a lovely filly and that (Cheveley Park) is the way we'll be heading. I would imagine usually if they are good enough they'd get a mile, and she's a big, rangy filly - she looks more like a three-year-old than a two-year-old."
O'Brien also commented further on the virus that has afflicted his yard in recent weeks.
He said: "It was in all of our three yards. It was as bad as we've had at Ballydoyle. I think we're at the other side of it now, though, and the year is not over yet, but if there is a relapse the season is over."
Fairyland is a 20/1 chance with Sky Bet for next year's QIPCO 1000 Guineas. Racing PR Manager Michael Shinners said: "This was a welcome winner for Aidan O'Brien and she showed a terrific attitude to come out on top. She's earned the step up to Group One company in the Cheveley Park and that will tell us more about her Classic aspirations."