Belle Couture's biggest test ended in disappointment at Flemington as Black Caviar's half-sister slipped at the start and then ran last in Saturday's Spotless Plate.

The three-year-old won a maiden at Caulfield in her second start last month and was sent out one of the favoured runners on a downgraded track because of rain.

Belle Couture was fractious in the barriers and, according to jockey James Winks, slipped jumping away before never looking a winning chance.

Winks eased the $2.6 million yearling purchase down in the final stages as Longchamp Belle raced to a one-length win.

The jockey was concerned Belle Couture may have hurt herself at the start.

"She was a bit nasty in there (barriers) and wanted to burrow under, but that didn't worry me," Winks said.

"What worried me was at the start she slipped pretty bad behind and she couldn't even tack up."

Trainer Danny O'Brien said Belle Couture was "not too bad" on pulling up but said he would know more after vets examine the horse on Sunday morning.

The race was a tale of two Belles, as Longchamp Belle put herself in contention for a trip to Brisbane.

Trainer Jason Warren scratched two horses from the Flemington meeting when the track was downgraded to slow on Saturday morning but was confident Longchamp Belle ($13) would handle it and she defeated I'm Fearsome ($14) with 1-1/4 lengths to Good Music ($26) third.

"We knew this filly would love it but we scratched our two runners here later on," Warren's assitant trainer Mitchell Beer said.

"You never know, she might end up in Queensland for a little stakes race. On the back of that win, you'd have to say there's a good race in her."