The Palmer United Party (PUP) could yet have a third senator in parliament at the expense of the Australian Greens.

Glenn Druery, the political strategist dubbed the preference whisperer, says the battle for the sixth and last Senate seat in Western Australia will ultimately come down to a battle between PUP candidate Zhenya Wang and Greens senator Scott Ludlam.

"It just depends on how the last 40 per cent of the vote comes in," he told ABC radio on Tuesday.

The Greens, so far, have polled 10 per cent of the first preference vote, equivalent to 70 per cent of the required quota for election.

While the PUP has polled 5.2 per cent of the initial vote, it will benefit more than the Greens from the exhausted votes of the so-called micro parties.

"Think of it as a ripple in a pond," Mr Druery said of preference flows in the Senate race.

"A ripple at one end can cause an effect down the other."

Initially it was thought the Australian Sports Party would pick up the final seat.

The Palmer United Party is on track to pick up Senate seats in Queensland and Tasmania.