Counting is continuing in the undecided seat with LNP candidate Teresa Gambaro's lead over Labor incumbent Arch Bevis steadily falling.
The Australian Electoral Commission's (AEC) official tally website has moved the seat into their "close" list.
Ms Gambaro was leading by 657 votes yesterday morning but that had dropped to 382 by day's end as initial counting of postal votes fell Mr Bevis' way.
If Mr Bevis' strong performance in absentee and postal votes continues he should retake the lead from Ms Gambaro, leaving the seat to be decided on the remaining provisional votes.
Mr Bevis said there were still thousands of votes to be counted and he wasn't about to give up hope of retaining the seat he's held for 20 years.
"But the way in which the postal vote campaign and other things went, it's certainly some cause for optimism - we'll just have to wait and see," he told ABC Radio.
Victoria University mathematician and electoral analyst Professor John Zeleznikow said the seat of Brisbane was likely to determine the outcome of the election, because the AEC's other "close" seat Corangamite would most likely go to the Labour party.
If so, this would take the seat tally to 72 seats to the Coalition, 72 to Labour, four independents and one Green - with only Brisbane to be decided.
"The undecided seat of Brisbane will be the closest fought and could decide who forms government," he said.
