La Collina came with a rattling late run to take the Group One honours in the Coolmore Fusaichi Pegasus Matron Stakes at Leopardstown.
Chris Hayes brought the Kevin Prendergast-trained filly to challenge on the outside in the final furlong after Lily's Angel had looked like landing the spoils after taking the lead.
La Collina (25-1), whose last success came in the Group One Phoenix Stakes two years ago, got up close home to beat Lily's Angel by a head with Say third and the French-trained favourite Kenhope fourth.
It was an emotional first Group One win for Hayes, who said afterwards: "I can't speak, I'm fully choked.
"She's coasted around. I got good advice off Declan (McDonogh) before the race. It's unbelievable.
"I owe it all to the boss and to the owners. She's been in great form and I'm so grateful they stood by me."
Kevin Prendergast added: "She's very, very special. She's very genuine and everything came right for her today.
"She has plenty of guts and the only bad run she's had was the last day here when it was very heavy.
"She worked during the week with Gordon Lord Byron and he won at Haydock so that made us more confident.
"She did it well. We were a little worried about the ground getting too tacky before the race.
"We will probably go the Sun Chariot (at Newmarket), she was fourth in that last year, and after that who knows!"