The Greens' right-wing preference strategy in South Australia has come home to roost with a re-elected Sarah Hanson-Young gifting Tony Abbott's good mate and conservative Family First candidate Bob Day the Senate balance of power.

In an echo of Victorian Labor's botched 2004 deal that saw Steve Fielding elected ahead of Jacinta Collins, the pushing of the Senate button yesterday saw leadership aspirant Hanson-Young returned with anti-gay marriage advocate Day at five and Liberal Simon Birmingham at six. Day received 3.76% of the primary vote or 0.26 of a quota in the race, which was formally declared at Adelaide's Stamford Plaza hotel this morning.