Blond Me got up in the shadow of the post to land the Coral Distaff at Sandown for trainer Andrew Balding and jockey David Probert.
The recent Salisbury maiden scorer was a 10-1 shot stepped up to Listed class and was nearer last than first rounding the home turn.
She appeared to be going nowhere two furlongs from home, with Probert scrubbing along, but found another gear once in the clear.
Montalcino looked to have the race sewn up 100 yards from the finish, but Blond Me galloped all the way to the line to get up by a neck.
Bella Nostalgia was third.
Probert said: "She can get a little bit keen in her races but she's managed to settle quite nicely today.
"She won her maiden very nicely at Salisbury and loved that ground. It was kind of a matter of time when I was going to get there.
"Everything fell right for her and she's quite smart."
Balding said: "I think it's difficult for the handicapper to make an accurate assessment of a horse from winning a maiden. She did it quite impressively at Salisbury.
"The aim with fillies is to make them more valuable, so a Listed race was the way forward.
"She's been working nicely with older fillies and the owner is over from Australia, so I'm pleased for them.
"I haven't given it (future plans) much thought, so we'll see. She's going to stay a bit further and there will be some nice races down the line.
"She's the type of filly that would probably stay in training and do better at four."
