Ceiling Kitty claimed a fiercely-run Queen Mary Stakes at Royal Ascot for Tom Dascombe.
Although beaten on her first couple of starts, the youngster came good with victories in a Kempton maiden and a Listed race at York.
Dascombe had a much better fancied filly in the Group Two contest in the shape of Upward Spiral, but that one could only finish fourth as Ceiling Kitty claimed top honours at 20-1.
Showing plenty of speed from the outset, Richard Kingscote's mount passed the post with a length in hand over the fast-finishing Hoyam, almost breaking the course record.
Hairy Rocket was the same distance away in third.Dascombe said: "It's great not just for me but for Andrew Black (owner) who bred her as well.
"Richard Kingscote was fantastic. He didn't exactly pick her, she was picked for him, but he was pretty confident. She's as hard as nails.
"The other filly (Upward Spiral) has run brilliant it's just that there was nothing fast enough this side to lead her.
"I think Upward Spiral is the better horse but just not today. This is all about Andrew Black, he's been an amazing support to me and to get a winner here for him is amazing."
Looking to the future, Dascombe said of the winner: "She's now won a Listed race and a Group Two so it doesn't really matter what we do, but we'll have to give six furlongs a go now."
Black, co-founder of Betfair, said: "This is my first proper home-bred winner here, I claimed the mother for £17k, I'm speechless.
"I knew she was good so I put half of her up on Betfair as part of a competition.
"I guess when I put her up for the competition I didn't know she was as good as she was but then when we found out I felt quite good about it and the four people are here and have had an amazing experience."
Michael Bell said of Hoyam: "It was a very good run, maybe it would have been better to have had another run before this as she just lacked a bit of experience. She's a filly with a future and we'll look at the Princess Margaret or the Cherry Hinton."
Richard Hannon jnr said of the third, Hairy Rocket: "She's only tiny but she ran a super race and there were no excuses. Hopefully she'll win a nice race before the summer is out. Maybe the St Hughes at Newbury or the Cherry Hinton."