The campaign to keep Scotland in the UK has a nine-point lead over its rival, according to a poll.
The Panelbase survey suggests support for the union stands at 46%, up two points from May, while support for independence increased by one point to 37%.
But in a warning to the Better Together movement, the results show pro-independence supporters are more likely to take part in the ballot in September next year.
Ivor Knox, managing director of Panelbase, said: "If we include everyone who has told us which way they plan to vote, irrespective of likelihood, the No side has a more substantial lead of 58 to 42."
The poll of 1001 adults in Scotland was carried out for the Sunday Times and Real Radio.
It found that 94% of independence supporters said they are very likely to take part, compared with 87% of unionists.
Meanwhile, the SNP has seen its support increase by three points to 48%.
Among other constituency voting preferences, Labour support is unchanged at 30%, Conservatives remain on 13% and the Liberal Democrats slip by one point to 4%.
Regional voting intentions put the SNP up three points to 48%, Labour down two points to 25%, Conservatives unchanged at 13%, Greens still on 6% and the Lib Dems dropping two points to fifth place on 4%.
SNP party business convener Derek Mackay said: "This is an extremely encouraging poll for Yes and for the SNP. With just a single-digit gap between Yes and No, a swing of less than 5% is enough to put independence ahead.
"There is everything to play for. Yes supporters are more likely to vote than people currently on the No side, which may very well be down to the negative 'project fear' campaign failing to motivate even their own supporters."
On his own party's fortunes, he said: "Over six years into government, the SNP now has more support than the three anti-independence Westminster parties put together, which demonstrates trust and confidence in the record of delivery of the SNP Government."
A spokesman for pro-independence group Yes Scotland said: "The No campaign has used every scare story imaginable, but people are getting wise to their tactics now.
"As we move into a new phase of the campaign and people consider the two different futures on offer in the referendum, we are confident that more and more will see that only a Yes vote will deliver the more prosperous and fairer country that they want to see."
Blair McDougall, campaign director of Better Together, said: "It is hugely encouraging that, in a poll that is normally more favourable to the independence campaign, Better Together have extended our lead. More and more undecided voters are deciding independence is too big a gamble.
"For the Yes campaign this poll is further confirmation that their efforts to foster division are going nowhere. Before the Yes Scotland launch, support for independence was 37%. Today it is still 37%.
"There can be no room for complacency, though, and we need to fight for every vote. We need to ensure that the pro-UK majority of Scots turn up on referendum day."
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