A result in the Seat of Upper Hunter will not be known at least until Tuesday.
The Nationals' Dave Layzell maintained his lead with 52.5 per cent of the two-party preferred vote on Monday, while Labor's Peree Watson had 47.5 per cent, with 48.2 per cent of the vote counted.
Both sides agreed the outcome would be determined by the results of the Singleton pre-poll booth that contains 6500 votes.
"It's really too close to call before we see what's in the pre-poll vote," Ms Watson said.
In addition, there were 5000 postal votes and 21,000 pre-poll votes cast.
Electoral Commission staff spent the majority of Monday counting Upper House votes. They expect to turn their attention to the pre-poll votes on Tuesday.
The Nationals are hoping they can hold the two per cent swing that appeared during Saturday night's vote.
However, as counting in other close seats on Monday showed, pre-poll votes can change things dramatically.
At the close of voting on Saturday, Mr Layzell told his supporters he was feeling positive about the party's prospects of retaining the seat.
"(The results) look positive at the moment; I'm certainly not upset about where we are," he said.
Earlier in the evening, he referred to "some pretty awful things", which had occurred during the campaign.
"In the last few weeks the campaign really intensified. We have seen a lot of personal attacks and I have found that very confronting," he said.
"It's the first time I have had to deal with these sorts of personal attacks but, of course, that is politics. You've got to toughen up and take it knowing that I am the face of government in this seat."
Despite looking increasingly likely to hold the seat, Mr Layzell acknowledged the mood for change across NSW.
"We've seen a night of Armageddon across the state," he said.
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