Covert Love gave Newmarket trainer Hugo Palmer his first Classic when powering home in the Darley Irish Oaks at the Curragh.
Pat Smullen brought the daughter of Azamour to head long-time leader Together Forever a furlong from home and storm to victory by a length and three-quarters.
Together Forever roared off in front, but Smullen decided to lead the pack and it proved the right tactic as Aidan O'Brien's filly maintained the pace for a long way.
Covert Love (7-1), who was taking her winning run to four and was supplemented for the race, won readily from Jack Naylor, with 15-8 favourite Curvy third.
Smullen said: "We were very confident the filly would stay.
"All credit to Hugo, this filly was in serious form.
"Her stamina was unbelievable. There's more improvement in her.
"It's great to win a Classic here on your home track."