The jockey who rode the last mare to win two Cox Plates has thrown his support behind Winx to achieve the feat at Moonee Valley.

Sunline's jockey Greg Childs, who is now retired, says the Chris Waller-trained Winx is the deserved favourite and the horse he'd want to be riding in Saturday's race which is billed as a showdown between her and Hartnell.

Sunline won her first Cox Plate in 1999 and won by seven lengths a year later. She was also second in 2001 and fourth in her final start in 2002.

Winx is striving to become the fourth mare to win two Cox Plates, with Flight and Tranquil Star in the 1940s the others.

Victory on Saturday would put Winx in rare air.

"And then the following year would even be bigger," Childs said.

"She's the up and coming champ, and she needs to win this to be put on the same mantle as Sunline."

Childs doesn't have her in that category yet.

"She needs to win this and she needs to win overseas," he said.

Sunline won major races in her homeland, New Zealand, as well as Australia, and was successful in a Hong Kong Mile and placed in Dubai on World Cup night.

"To be a champion, you've got to win internationally," Childs said.

Winx is chasing her 13th straight win and ninth Group One trophy on Saturday, having won last year's Cox Plate by almost five lengths.

"Winx deserves to be the favourite," Childs said.

"She's a superstar in the making. And she's my tip because she's a proven galloper around Moonee Valley.

"Not a lot of horses can improve around a corner and win. She's proven she can do that where Hartnell, even though he has raced well there, he hasn't won there.

"So that's the advantage she has over him. But tactics are going to be important because there is no natural leader.

"I'd want to be on Winx and I'd be wanting to be in the first three, because the tempo of the race might be slow.

"And if it's fast you can get back a little bit more.

"But whatever it is, I'd rather be in front of Hartnell than behind him."

Many are anticipating a classic contest between two horses seemingly at the top of their games.

"I hope it is," Childs said.

"Like everyone, we just want a two-horse war."