Liber Nauticus staked a claim for the Investec Oaks when she got on top close home to land the Tattersalls Musidora Stakes at York.
The 4-6 shot hit the front about a furlong and a half out and kept on strongly to beat Romantic Settings by a length and a half, with Woodland Aria just behind in third.
The Michael Stoute-trained filly, ridden by Ryan Moore, was having only her second career start following a debut success at Goodwood last September.
Moore said: "I was very happy with her because she doesn't actually do a lot.
"She only does enough, so I was very happy.
"Hopefully she'll get better as she gets older."