Her trainer has been preparing for the day Winx gets beaten and for a couple of seconds at Moonee Valley it seemed he might need to steel himself.

But such are the champion qualities of Winx, Chris Waller can now breathe easy after she held off the challenge from Humidor to win a record-equalling third Cox Plate on Saturday.

"We've all been prepared for the day she gets beaten," Waller said.

"We are ready for anything."

But like everyone else at the track, Waller was more prepared for Winx to win with the mare at $1.18, her shortest Cox Plate price.

He watched the race in the quiet of the weighing room and with no perceptible change to his demeanour.

But he admitted it was a relief.

"I was concerned for a moment down the straight but she is Winx," he said.

"She finds a way to win like all champions do.

"She's unbeaten for almost three years now and I'd be lying if I said I didn't go to bed at night thinking of her record."

Her record now stands at 32 starts for 26 wins, 22 in succession and 15 at Group One level. Her prize money is a tick over $15.6 million, an Australian record.

After racing three-wide midfield from around the 1100m, Winx went to the front at the top of the straight and looked as if she would cruise to the line as she has for the past two years.

Blake Shinn had other ideas on Humidor ($31) and chased hard, coming to within a long neck and forcing the mare to better the record 2min02.98sec she set for the 2040m in her first Cox Plate by .04sec.

English horse Folkswood ($26) held third, 4-1/4 lengths behind Humidor after racing on the pace set by Gailo Chop while three-year-old Royal Symphony ($19) was fourth.

While Waller admits there is pressure associated with a horse like no other, her jockey Hugh Bowman is ever cool even if he is churning inside.

"I'm lost for words," he said.

"She's made history. I was born the year Kingston Town won his first Cox Plate and to think she's emulated him.

"Trying to compare one horse to another is hard.

"They're all different animals at the end of the day. But we are in the presence of greatness. She'll be recognised as one of the greatest horses to grace the Australian turf.

"To be a part of her career, I can't explain how much that means."

Bowman is the country's leading Group One jockey, and Waller is Australia's leading Group One trainer.

Humidor's trainer Darren Weir has grown his stable over the past five years to be a serious challenger and already has a Melbourne Cup win with Prince Of Penzance in 2015.

He will aim for another with Humidor who ran fifth in last week's Caulfield Cup and backed up because the trainer was unhappy with how he was ridden.

"Blake rode him how we wanted him ridden last week," he said.

"It was a great run today, but I'd rather we'd won."

Plenty are glad he did not.