Above The Curve dug deep to fend off the late charge of Insinuendo in the Moyglare “Jewels” Blandford Stakes at the Curragh.
A Group One winner at ParisLongchamp when last seen in May, Above The Curve was a 5-1 shot for Joseph O'Brien and Ryan Moore, with last year's victor La Petite Coco the even-money favourite for the 10-furlong feature.
Moore settled on the outside of La Petite Coco and was perfectly positioned to go for home when the favourite tried to launch a winning run a couple of furlongs out.
Above The Curve grabbed the lead and refused to relent, holding off the fast-finishing Insinuendo by a neck, with 66-1 shot Galleria Borghese a further length and a quarter back in third.
"I thought it was a fantastic ride from Ryan. It was the filly's first run back after a lay-off and I thought she'd come on a bit for the run," said O'Brien.
"She's a classy filly, a Group One winner, and I think her attitude really showed in the last 100 yards, she put her head out and fought it out.
"She's an impeccably-bred filly and I've been really lucky with the American Pharoahs, he's done really well here in Europe particularly.
"You could see this filly's attitude in the last furlong – when the going was getting tough she put her head out and fought all the way to the line, beating a very good filly.
"The plan was that this would be a nice stepping stone to the fillies' race on Arc day (Prix de l'Opera) and that should set her up lovely for that, she's a course and distance winner already."
When asked if she could remain in training next year, he added: "I think there is a chance that could happen. She's a big filly, she's actually 17 hands which for a three-year-old filly is incredible.
"She seems to have progressed from the spring and hopefully she can progress in the future."
Dexter Belle sprang a 50-1 shock for Edward Lynam in the Irish Stallion Farms EBF "Bold Lad" Sprint Handicap.
Rough Diamond appeared to be the trainer's first string, but it was Dexter Belle in the hands of Andrew Slattery who hit the front in the dying strides to prevail by a neck, with just a head and a nose separating the placed horses No More Porter, My Wagyu and Laugh A Minute.
When asked if it was a surprise, Lynam said: "Possibly when Chris (Hayes) picked the other one. I loved her when I got her and thought she was well handicapped.
"She ran a bit disappointing for me, but OK, on Guineas weekend but then she ran a stinker next time, it was desperate but my horses were out of form."
