Aidan O’Brien feels stepping Opera Singer up to a mile and a quarter for the Qatar Nassau Stakes should be “really interesting”.

The champion juvenile filly last year when she won the Prix Marcel Boussac by five lengths, she was denied a run in the 1000 Guineas due to a setback in the spring.

O’Brien got her back in time to run in the Irish equivalent but due to the time she had missed, he expected her to improve markedly for the run.

The fact she finished third to Fallen Angel there surprised O’Brien and she did take a huge leap forward at Royal Ascot when finding only multiple Group One winner Porta Fortuna, trained by his son, Donnacha, too good in the Coronation Stakes.

That form has been franked by the winner in the Falmouth Stakes, and with Opera Singer being by American Triple Crown winner Justify, O’Brien expects 10 furlongs to suit.

“Obviously she is stepping up to a mile and a quarter from a mile for the first time and we think that is going to be really interesting,” he said.

“We were delighted with her at Ascot, really. That was just her second run and, to be honest, we couldn’t believe how well she’d run first time in the Irish Guineas, given the setback she had in the spring.

“We thought her Ascot run was very good and obviously the form has been franked as Donnacha’s filly came out and won the Falmouth at the July meeting. She’s an exceptional filly, so she lost little in defeat.”

Opera Singer is in receipt of 8lb from her chief market rival, the John and Thady Gosden-trained Emily Upjohn.

Now a five-year-old, she is without a win since last year’s Coronation Cup, where she beat subsequent King George and Arc runner-up Westover.

She did, though, need to be supplemented for the race at a cost of £40,000 after connections decided to stick to 10 furlongs following her good effort in Ireland when just reeled in by Bluestocking.

“She wasn’t entered originally because the plan was to go for the Pretty Polly and then maybe go on to Ascot for the King George, but we decided after the Curragh to stay at a mile and a quarter and go against the fillies again, then step her back up to a mile and a half again in the Yorkshire Oaks,” said John Gosden ahead of the next leg of the British Champion Series.

“Emily Upjohn is in good form. She’s a top-of-the-ground filly and she ran a great race at the Curragh, but that rain came and she’s not happy on it. She’s won on it, but it’s not her best surface. All being well, she’ll run a big one.”

Elmalka was a surprise 28-1 winner of the 1000 Guineas but was then only fourth to Porta Fortuna at Ascot, prompting the step up in trip by Roger Varian.

“We’re looking forward to running Elmalka, she’s really well and she looks like she is ready to step up to 10 furlongs,” said Varian.

“It will give us some direction for the autumn and we entered her for the Prix de la Opera this week and she will probably have an entry back at a mile in the Sun Chariot – and depending on how she runs in the Nassau, we’ll get some direction moving forward.

“She’s in great form and has done nothing wrong all year, even her run at Ascot was a great run under the circumstances, so we’re very excited to run her. It looks a strong race but we decided to get her out again.”

Ralph Beckett runs two, Doha, a daughter of Treve, and Lady Boba, who is dropping in trip after two runs over a mile and a half.

Beckett said: “Lady Boba drops back to a mile and a quarter for the first time this year. I thought she travelled really well and perhaps didn’t quite get home when third in the Lancashire Oaks last time. She’s a stakes winner over a mile and a quarter and she’s in very good shape.

“Doha is owned by the sponsors and was a bit unlucky last time in the one-mile Listed race at Pontefract, where she was tight for room at a crucial stage and then ran on well to finish a close second to Caernarfon, who got first run on her.

“I’ve always felt that a mile and a quarter would be better for her – she’s bred to get a mile and a half – so I’m looking forward to her too.”