Australia's reigning Horse of the Year Winx has been installed odds-on favourite to win Sydney's richest race in the autumn.

The TAB has opened its market on the $4 million weight-for-age Queen Elizabeth Stakes (2000m), which is run at Randwick in April, with the Chris Waller-trained champion mare Winx at $1.80.

Winx has not been beaten since her second in the ATC Australian Oaks in April last year, winning her past 13 starts including the 2015 and 2016 Cox Plates at Moonee Valley.

Winx won her second Cox Plate last month by a record eight lengths before she was sent for a spell.

She is the $2.80 favourite to join Kingston Town as the winner of three Cox Plates.

Hartnell, second in the Cox Plate and third in the Melbourne Cup, is at $11 for the Queen Elizabeth ahead of Omei Sword and The United States at $15.