The Australian bid for a second successive Diamond Jubilee Stakes at Royal Ascot on Saturday stayed alive for a large part of the 1200m of the race, only to fade and fail at the crucial time.

A year to the day after Black Caviar scored the most controversial win of her impeccable career in the same race, Sea Siren did her best to emulate.

But, after being in front early among the leaders until the 900m mark, Sea Siren's bid unravelled when the pressure went on.

"She came here fit and well, but she wasn't good enough on the day," said trainer John O'Shea.

A three-time Group One winner at home, Sea Siren was making her second attempt to win a major international race and produced a similar effort to the one she turned in Hong Kong last December.

Sea Siren finished eighth of the 18 runners, a result that, on paper, ranks as one the worst of her life.

Certainly jockey Ryan Moore didn't press her when it became obvious she had no more to give.

For O'Shea and the mare's new part-owner, Ireland's Coolmore Stud, the result was a bitter disappointment.

"It's always difficult to travel, you never know exactly how they have coped," O'Shea said of the long flight.

The Diamond Jubilee, a race in which Australian horses other than Black Caviar have fared well, went to the local galloper Lethal Force.

Sea Siren's defeat followed that earlier in the week of Shamexpress who finished a well beaten ninth in the King's Stand Stakes on Tuesday.