Nash Rawiller will partner Southern Speed in the Melbourne Cup as the pair try to turn their spring carnival fortunes around.

Glen Boss sacked the mare after her sub-par performance in the Turnbull Stakes and Rawiller chased the ride on Southern Speed for her Caulfield Cup defence only to miss out when she was withdrawn on race eve due to her wide barrier.

She instead went to Saturday's Cox Plate in which she was an eye-catching sixth with Luke Nolen aboard, again from a wide draw.

That run convinced trainer Leon Macdonald she would be a worthy Melbourne Cup contender and the decision was made to give her a chance.

"Last week I was against running her in the Melbourne Cup but the way she finished the race off yesterday has changed my mind," Macdonald said.

"She seems to be racing a bit dour and her final sectionals were very impressive.

"Nash will ride her in the Cup."

Rawiller's Cox Plate was a disaster with any plan Gai Waterhouse had when she selected barrier 11 for More Joyous out the window before the first turn.

With first Happy Trails and then surprise packet Ethiopia kicking up to take the lead, More Joyous was six-wide with nowhere to go and eventually weakened to finish 11th of the 14 runners.

Southern Speed came from last on the home turn to run the fastest final sectional times of the race.

Australian Derby winner Ethiopia held on for fourth in the Cox Plate after Rhys McLeod's daring tactics and like Southern Speed, will be paid up at Monday's next acceptance stage for the Cup.

Although her best performances have been at middle distances and the 2400 metres of last year's Caulfield Cup, Southern Speed has breeding on her side when it comes to stamina.

Her mother Golden Eagle is by Zabeel, the sire of two Melbourne Cup winners and last season's champion broodmare sire of Australasia.

Zabeel's presence will be felt against the dominance of European bred stock in the Cup with his sons Maluckyday and Zabeelionaire looking to join Might And Power (1997) and Jezabeel (1998) as winners of the race.