Saoire held off Penkenna Princess in a thrilling finish to win the Irish 1,000 Guineas at The Curragh on Sunday.
Ridden by Mick Kinane, the 10-1 chance just edged the Ralph Beckett-trained British challenger Penkenna Princess with Luas Line just behind in third.
It was a first Classic success for Irish trainer Frances Crowley, who is married to leading jockey Pat Smullen.
Smullen rode Utterly Heaven, the fourth filly home in the one mile contest, worth £155,000 to the winner.
And the jockey won the other big race of the day at The Curragh, the Tattersalls Gold Cup.
Saoire was always up with the pace and moved into the lead in the final furlong.
But Penkenna Princess fought back and there was nothing between the pair at the line, with the judge taking several minutes to announce the official result.
English 1,000 Guineas winner Virginia Waters, who was sent off the 11-10 favourite, but never threatened.
Crowley is best known for her jumping horses and has never even had a Group winner on the Flat.
"Recently I have been trying to concentrate more on my Flat horses and this is brilliant," said Crowley, who said Saoire could now head for the Oaks at Epsom.
"I've always thought of her more of an Oaks filly than a miler. She really appreciated the ground today and we will have to consider going to Epsom, although there is always the Irish Oaks back here in July."
Saoire was slashed to as short as 10-1 for the Oaks.
Boylesports Irish 1,000 Guineas (Grade One)
One mile, The Curragh
1 Saoire (M J Kinane) 10-1
2 Penkenna Princess (S Sanders) 25-1
3 Luas Line (W Lordan) 20-1
18 ran. Dist: Shd, ½l.