Sheehan shot a 3-under-par 69, following rounds of 69-66, to get 12-under for the tournament. He leads Tony Carolan of Queensland by one and is two clear of Leith Wastle(67), Craig Carmichael(67) and Andrew Buckle(68).
Overnight leader Peter Senior, also from Queensland, carded a 1-over 73 and fell three strokes off the lead to 9-under par.
Four other players are tied with Senior at 9-under and four more players are four back at 8-under.
Thirteen players in all are within four shots or less and will head into Sunday's final round looking to win the $100,000 first-place check.