The well-backed Misty For Me (5-1) just got the better of stablemate Together to win the Etihad Airways Irish 1000 Guineas at the Curragh.
Aidan O'Brien won the 2000 Guineas 24 hours earlier with Roderic O'Connor and, just like the colt, Misty For Me had badly disappointed in the English equivalent.
However, Seamie Heffernan got a great tune out of his mount inside the final furlong and she battled on gamely to claim the scalp of luckless stablemate Together, who was also second at Newmarket, by three-quarters of a length.
Just behind the two O'Brien runners was Jessica Harrington's Laughing Lashes, who was another to return to her smart two-year-old form after flopping in the English Guineas.
O'Brien said: "She's always been a very good filly and she stays well. The plan for her was to come here and then on to Epsom for the Oaks. Together is likely to go for the Coronation now.
"Last year Misty For Me won on all grounds, so I was puzzled by her run at Newmarket. I knew the ground wasn't the cause and it seems she just didn't fire on the day. Seamie knows her very well and gave her a great ride and she is a tough, hardy filly.
"The fact that Roderic bounced back and won on Saturday gave us hope. They were both very well going over and have been very well since, so it may just be that they both needed their first runs."
Heffernan added: "I wasn't exactly confident going into the race until I saw Roderic O'Connor win.
"Aidan said to ride her positively and I'd won a Group One on her last year so I knew how good she was. We had a bad draw, but good horses tend to get you out of trouble.
"I saw Ryan making his challenge and I'd not gone for everything on mine until I had to. I've ridden Together at home so I know how good she is, but Misty For Me is probably the more straightforward of the two. It's emotional winning a Classic - there's only five a year."