Damien Oliver has named Master O'Reilly as the biggest threat to Purple Moon's bid for Emirates Melbourne Cup glory.
The pair have dominated the market for Tuesday's Flemington showpiece in recent weeks, with local runner Master O'Reilly just shading it as the general 4-1 favourite.
Luca Cumani's Purple Moon is a best-priced 11-2 with VC Bet and although Oliver believes the British raider has a definite place chance, he expects the Caulfield Cup winner to provide a stiff test.
"He's been the obvious one from pretty early on. He's well weighted and he's in great form," said the rider, who will be teaming up with Purple Moon for the first time.
"It looks like he stays well."
Oliver was also optimistic about the hopes of Aidan O'Brien's St Leger runner-up Mahler.
"He's got no weight on his back and he's going to be up on the pace and out of trouble," added Oliver.
"The only thing you don't know about him is being a three-year-old how he's going to cope and he hasn't raced here yet."
O'Brien is well aware of the challenges of both Master O'Reilly and Purple Moon, with his Honolulu having finished second behind the latter in the Ebor at York.
"He's a very classy horse. Luca will have him spot on," said O'Brien.
"He stays well, handles fast ground and has some class so I think they're going to be the two big horses."
Mahler won the Queen's Vase at Royal Ascot earlier this year so O'Brien has no doubts about his stamina over a strongly-run two miles.
"He won a two-mile race at Ascot which would be a lot stiffer track than Flemington," he added.
Jockey Stephen Baster rides the Irish colt for the first time and said: "I think he's quite quick out of the machine (stalls).
"The feeling he gave me, I think he'll stay the two miles and with the 50.5kg on his back, he'll be able to free-roll up on the speed somewhere and he'll run the two miles right out."
O'Brien, who saddled Yeats to finish seventh last year, is hoping Mahler will develop into a top-class stayer as a four-year-old and is pleased to be taking his chance off a low mark this term.
"(In) our experience of weights with top-class stayers, they automatically get top weight here," he said.
"We felt that if everything went according to plan and we came back next year, he would have top weight rather than bottom weight."
Master O'Reilly's trainer Danny O'Brien respects the challenge of both Purple Moon and Mahler, while rating Maybe Better and Zipping as Australia's best chances outside of his runners.
"Without the Japanese horses they would have run one two last year," he said.
"I'm really happy that in the biggest race of his life, Master O'Reilly's going to be the greatest shape of his life."
The track at Flemington was rated as slow on Monday and with no further rain expected to fall leading into the race, course manager Terry Watson was confident of dead going on Tuesday.
"If this weather stays up the way it is and we don't get any more rain, I feel sure it'll get to dead tomorrow," Watson said.
"If the track does come up dead I don't think dead really affects any horse's chances whether they like it firm or soft.
"I think it's the middle ground that should suit everyone."