Lillie Langtry swooped well inside the final furlong to take the Coolmore Fusaichi Pegasus Matron Stakes at Leopardstown for the Aidan O'Brien yard.
Settled in rear by Johnny Murtagh as Gile Na Greine led the way in the Group One contest, she was brought to the outside to challenge in the straight.
Kieren Fallon took over and made the best of his way home on Spacious, but Lillie Langtry (7-2) made relentless progress and struck the front in the closing stages to win by a neck, with Music Show a close third.
O'Brien said: "Johnny gave Lillie Langtry a masterful ride - the filly didn't know she had a race and was only asked to race properly in the last furlong and a half. It was a peach of a ride.
"She is a very determined filly and was always very classy. Her next race will be in the Prix de l'Opera in France."
