Mizzava turned over Giant's Causeway's half-sister Hanky Panky in a surprise result to the Irish Stallion Farms EBF Fillies Maiden at Limerick.
Michael Halford's filly was sent off at 25-1 after being well beaten on her only previous start, but she stepped up considerably to open her account at the expense of Aidan O'Brien's runner.
Bethany Bay forced the issue to just over a furlong out where the smooth-travelling Hanky Panky hit the front and looked set for victory, despite Joseph O'Brien putting up 1lb overweight.
However, Shane Foley had other ideas and delivered Mizzava with a well-timed to run to head the 9-10 favourite close home and win by three-quarters of a length.
Halford said: "On her first run at Dundalk she needed it and she was a bit lost around there. I was a bit worried she might be caught out by lack of fitness as she's a bit lazy at home. She's smart enough and holds an entry in the Irish 1,000 Guineas. There will be worse than her in it."
O'Brien gained some compensation for Hanky Panky's loss when Marchese Marconi atoned for last week's expensive Dundalk defeat with a workmanlike victory in the Festival Of Speed Maiden as the 2-7 favourite.
The Ballydoyle handler followed up when El Salvador (15-8) couldn't be caught by Irish Cesarewitch winner Voleuse De Coeurs in the Summer Twilight Nights Race.
Pat Smullen was seen at his strongest to get Diesel Ten (7-1) home in front in the UL Racing Society (C&G) Median Auction Maiden. Dermot Weld's gelding rallied gamely when headed by Hold The Line to regain the lead in the dying strides.