Trainer David Payne has continued his wonderful vein of form this spring with Costello upsetting his more fancied rivals to win the $500,000 Rosehill Gold Cup.

The $40,000 yearling purchase took his earnings to just under $600,000 with Saturday's victory and Payne was delighted that he struck a wet track at the right time.

"His last run was on a good three and Tommy (Berry) came in and said, 'David, he's feeling it, keep him on a soft surface' and that's why we haven't run him," Payne said.

"As soon as it rained I threw him in this race. I didn't think he'd get a run to be honest.

"But once we got in with 54 kilograms and then we drew one I thought, he's in with a shout."

With only 25 horses in work, Payne has been in a purple patch of form.

The former champion South Africa trainer also saddles up favourite Montefilia in Thursday's VRC Oaks at Flemington after she claimed the Group One double of the Flight and Spring Champion Stakes during the Sydney carnival.

"With my little string it's been very good," Payne said.

Winning hoop Jay Ford was full of praise for Costello after his first ride on the Americain gelding.

"He's a quirky animal and he likes to do things his way but he gave me a lovely ride," Ford said.

"The speed was nice and I was able, from a good gate, just to conserve our energy all the way. He switched off at the right time."

Costello ($31) ploughed through the heavy conditions to claim Saturday's 2000m race by a neck over the fast-finishing She's Ideel ($5) and Morton's Fork ($31).