Fading Coalition hopes of passing the union-taming legislation used as trigger bills to force the July 2 double dissolution election were given a boost on Tuesday but the numbers still look tight even if both houses are counted as one in a special joint sitting.

In a surprise result at the end of counting in South Australia's Senate race, the anti-union Family First senator Bob Day has emerged as the 12th senator from the central state, displacing Labor's fourth spot and thus ending the career of Anne McEwen.

The final result in South Australia is: Liberal 4, Labor 3, NXT 3, Greens 1 (Sarah Hanson-Young), Family First 1.

A former housing industry entrepreneur, the conservative Senator Day secured his term with just 0.37 of a quota of first preferences. His return on favourable preference flows, adds to the numbers in favour of the government's Australian Building and Construction Commission and its Registered Organisations bills.