Bluesea Cracker, trained by James Motherway, landed an incident-packed renewal of the Powers Whiskey Irish Grand National at Fairyhouse.
There were plenty of casualties in the three-mile-five-furlong contest, including favourite Saddlers Storm, leading fancy Telenor and British raider Double Dizzy.
Bluesea Cracker (25-1) was well to the fore as the field rounded the turn for home for the final time and although she began to tire on the run-in, Andrew McNamara's mount had enough in reserve to repel the challenge of Oscar Time by four and a half lengths.
Whatuthink was third, with Cheltenham cross-country winner A New Story fourth.
It was the biggest success in the career of Cork-based Motherway - and the trainer's first over fences this season.
The handler said: "I can't believe it. She's been a fantastic mare for us. I walked the track at 12pm and was worried about getting home in the ground. I skipped a heartbeat going to the last but then jumped six feet into the air after it!
"We found that she has been far more settled this year and if she was ever going to go for an Irish National it was this season.
"All credit to Andy. I wanted to drop in, but he said he wanted to be mid-division as they wouldn't be gaining much ground in the conditions. He's a cool man and he waited for the last minute until he had to go. He lifted her over the last three."