Australia, the hot favourite, will have to defy stall 12 in a field of 16 for tomorrow's Investec Derby, the biggest assembled since 2008.

Aidan O'Brien's regally bred colt has been a warm order for the blue riband Classic ever since beating the highly-regarded Free Eagle last September. He was beaten on his return to action this season in the Qipco 2000 Guineas, but his pedigree suggests he can only improve for stepping up in trip.

The fact that two of the three horses to have run from the 2000 Guineas have won the Irish Guineas and the Dante and French Derby, in Kingman and The Grey Gatsby, also gives him solid claims. As well as a big field and wide draw, though, Australia may have to overcome softer ground than ideal with heavy showers forecast.

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Andrew Cooper, the clerk of the course, said: "We've had a lovely drying day and the going is predominantly good with the odd softer patch, I'd say we're heading towards good for the Oaks. Potentially there is rain forecast for Saturday, but how much confidence you place in those forecasts I don't know."

A win for Australia would be bad news for William Hill who have him as 11-8 market leader and also report strong support for stablemates, Geoffrey Chaucer and Orchestra. "Australia is clearly the worst result in the book, but the money has come for his stable companions, with Geoffrey Chaucer and now Orchestra," said William Hill spokesman Jon Ivan-Duke.

Last year Joseph O'Brien chose to ride Battle Of Marengo only to see Ryan Moore partner stablemate Ruler Of The World to victory, but there was never any doubt he would be on Australia this time. Moore is on Geoffrey Chaucer, while Seamie Heffernan rides Orchestra and Colm O'Donoghue is on Kingfisher.

The Sir Michael Stoute-trained Snow Sky will not run after failing to recover from a minor setback.

There is a strong Irish challenge outside of the Ballydoyle quartet, with the first two home in the Derrinstown taking their chances. John Oxx's Ebanoran was first past the post that day but Dermot Weld's Fascinating Rock was awarded the race by the stewards after the pair got very close in the finish. Oxx has only had three runners in the Derby, but has won it twice.

He said: "I can't really make any comparisons with my two Derby winners (Sinndar and Sea The Stars) as it is too early - Ebanoran has not won a significant race yet. He is quite an idle worker at home, like Sinndar, so doesn't give us too many clues about the extent of his ability."

The daughter of Sea The Stars, Taghrooda, shot to the head of the betting for today's Investec Oaks after a thoroughly dominant display in the Pretty Polly Stakes at Newmarket on just her second start but that form has not really stood up.

Her owner Sheikh Hamdan Al Maktoum's last Group 1 win in Britain was nearly five years ago but he has major chances with the aforementioned and also Tarfasha.

Angus Gold, the Sheikh's racing manager, said: "Everyone has crabbed [Taghrooda's] form and of course you'd love to see it work out but it doesn't mean she's not progressive. Sometimes the style [of victory] is more important."