Isabella Giles continued her progression with a decisive victory in the Shadwell Rockfel Stakes at Newmarket.

Successful on her first two starts at Leicester and Newbury respectively, Clive Cox’s filly came up a little short when bidding to complete the hat-trick – finishing fourth in the Princess Margaret Stakes at Ascot.

However, a step up to seven furlongs for the first time saw her claim Group Three honours in impressive style in last month’s Prestige Stakes at Goodwood – and she was an 11-5 chance stepping up to Group Two level on the Rowley Mile.

Aidan O’Brien’s even-money favourite Monday was sent to the front from the off by Ryan Moore, but it was clear from the halfway stage that she was struggling – and Isabella Giles took over the lead with relative ease in the hands of Adam Kirby.

The result was scarcely in doubt from that point, with the daughter of Belardo finishing strongly to prevail by two lengths from Nazuna.

Cox said: “It was on better ground today, and more rain wouldn’t have been a concern.

“She put up a very classy performance and has got a wonderful temperament. She settles into a lovely rhythm and she can find her own way in a race.

“She doesn’t have to lead, but she is so relaxed that finding a rhythm and setting your own fractions worked perfectly. Adam got his fractions right, and she made a good job of it.

“I think she is definitely a filly to get a mile next year, which is really exciting. I’m delighted for Clare and Paul Rooney to have such an exciting possibility as a Classic contender. I’m over the moon.”

The Lambourn-based trainer confirmed a return to Newmarket for the Fillies’ Mile as an option.

He added: “She is very well balanced. She has won at the track. She is a filly that has a little bit of scope, that is well balanced and has got a wonderful mind and clearly a big level of ability.

“She is in the Fillies’ Mile, but she has done pretty good this year. She wouldn’t have blown a candle out there, but we will see how she comes back.

“It was a ‘win and you’re in’ race for the Breeders’ Cup, but I’m not sure. Next year beckons over a mile, and I think we will be looking that way.”

Roger Varian was delighted with the performance of the runner-up Nazuna.

He said: “She is a lovely filly, and we were not here just to make up the numbers. I really like this filly and I’m delighted she has run up to our expectations.

“Andrea (Atzeni) thinks she will stay a mile, and there are lots of nice options – there’s the Oh So Sharp Stakes back here in a couple of weeks or there is the Breeders’ Cup Juvenile Fillies’ Turf, which is a race we were second in with Daahyeh last year after winning this.”