Greens senator Sarah Hanson-Young has secured top spot on the party's South Australian senate ticket, leaving Robert Simms at risk of losing his job.
Greens Senator Robert Simms admits he has a fight on his hands to secure re-election after placing second on the party's South Australian Senate ticket.
Party members voted Sarah Hanson-Young to the top spot, leaving Senator Simms likely dependent on preferences to retain his seat.
The Greens won seven per cent of first preference Senate votes in SA at the 2013 election.
In order to get both senators re-elected at the double-dissolution election expected to be called for July 2, the party must lift its vote to about 15 per cent after preferences.
"There is absolutely no doubt in my mind that we can do it," Senator Simms told AAP on Monday.
"Commentators said Sarah Hanson-Young wouldn't get elected in 2007. They wrote Sarah off again in 2013.
"The Greens in SA have confounded the critics every time and I expect them to do so again."
Senator Simms said his progressive values were more in line with voters in SA than conservative candidates such as Family First Senator Bob Day.
He also took aim at the Nick Xenophon Team, which is tipped to compete with the Greens for voters disillusioned with the major parties.
"There's no question that Senator Xenophon is a big force in South Australia but he's just one person on this ticket," Senator Simms said.
"There's a range of other people who don't necessarily have Senator Xenophon's proven track record in public life."
Flinders University political scientist Haydon Manning said the Greens were a chance of getting two senators elected if the Nick Xenophon Team vote was lower than expected.
"It's possible part of the wind has been taken out of Xenophon's sails with the submarines contract being the full compliment of what was promised," Prof Manning told AAP.
"The other side of the coin is maybe voters will see he deserves to be rewarded."
Prof Manning said it was likely several senators in SA would be elected without a full quota, making the distribution of preferences vital.