Moonlight Rock came from last to first to claim the mile handicap at Dundalk under Kevin Manning.
The Paul Deegan-trained filly was produced with a strong charge inside the final furlong.
The 12/1 shot got to the front inside the final 100 yards to record a length-and-a-quarter success over Boynagh Joy
"That's a bit of a surprise. Her best form has been up to six furlongs and a couple of the lads who rode her weren't sure of her trip," said Deegan.
"Kevin gave her a great ride. He dropped her in and kidded her along. He took her back at the start and that suited.
"He said she did everything well. She travelled and he knew turning in she'd take a bit of beating.
"Hopefully there is another one in her. She was highly rated. I ran her in a Listed race last year and I suppose you get what you deserve. She's on a realistic mark now."
