IT WAS the biggest day of Sydney's autumn racing carnival and the star-studded crowd turned traditional race fashions on their head.

Odds-on favourite in the style stakes for yesterday's Derby Day at Randwick racecourse included classic top hats and fedoras - but the look was sported by the fillies.

The Bart Cummings-trained Roman Emperor won the famous race in a photo finish, watched by a crowd of 30,000.

Newsreader Samantha Armytage led the fashion pack, teaming a top hat with a Lisa Ho dress. "It is a bit out there," she said. "I was going to wear an Akubra - I am a country girl - but then it evolved into a top hat."

Designer Nicky Zimmermann was forced to drink her glass of champagne through a straw, as her avant-garde Nerida Winter fedora sprouted long feathers which obstructed her face.

Television stylist Kelly Smythe and model Siobhan Parekh wore matching man-style fedoras, while model Erin McNaught trialled edgy, elbow-length, fingerless gloves.

Not everyone had backed the right colours on the traditionally black and white day.

Megan Gale told the mostly monochrome crowd at the David Jones marquee: "The one exception is my boyfriend [radio host Andy Lee]. He said, 'Babe, you're lucky you're getting me in a suit. It's blue."'

Horse trainer Gai Waterhouse also bucked tradition, wearing bright canary yellow.

Traditionally, men are expected to don morning suits, tails and top hats on Derby Day, with the vintage headwear recently resurrected in Europe.

"Last year, [top milliner] Philip Treacy did top hats and it started to cascade down here right now," said Sydney hat maker Donny Galella.

For some punters, the fashions provided more entertainment than the on-track action.

Mel Elliott, a 23-year-old from Hunters Hill, said: "I forget there's even horses here."

Evidence of a recession was scarce at the Emirates marquee, which had an Austrian theme. Guests were served an estimated 6000 glasses of wine, 40 kilograms of veal schnitzel and 30 metres of apple strudel.