Winx has been described as "picture perfect" by trainer Chris Waller on the mare's sixth birthday ahead of her shot at a 20th straight win at Randwick.

Winx has drawn barrier one in the George Main Stakes where she will again be up against Red Excitement on Saturday after powering past the gelding to win the Chelmsford Stakes after he set up a big lead mid-race.

"Red Excitement had quite a break on us but when she spotted that horse in front she really motored at him," jockey Hugh Bowman said.

"I could feel her will to win and her tenacity to be first past the post and for me that was very special".

The Group One 1600m weight-for-age race at Randwick on Saturday is another step towards the Cox Plate for Winx.

Trainer Chris Waller is hoping the mare will match the record currently held by Kingston Town when she competes in her third Cox Plate win in October.

"Winx is like Usain Bolt, he does not look like the winner at the 50 metre mark, it's the last 30 metres that he really starts to excel" Waller told AAP.

Tributes have been pouring in on social media for the superstar mare who celebrates the afternoon of her sixth birthday munching on hay among the quiet of her home turf at Rosehill.

"Here's to you Winx! You are a superstar! Happy birthday!" the team at Chris Waller racing posted on its Facebook page.

By Street Cry, Winx was born in the Hunter Valley in NSW on September 14, 2011 to Vegas Showgirl and is now ranked second in the world to American dirt specialist Arrogate.

Her win in the Chelmsford Stakes equalled the 19-race winning streak of another American superstar, Zenyatta whose only defeat came at her 20th and final start when she failed by a short head to catch Blame in the Breeders' Cup Classic.

Winx is at $1.08 to defend her title in the George Main with Happy Clapper at $11, her stablemate Foxplay $14 and Red Excitement $19.

Foxplay looked as if she would win the Warwick Stakes, Winx's first start of the preparation, but the great mare ran her down after missing the start by four lengths, prompting Waller to race her in earmuffs.