It was the first time a mainstream poll had suggested the pro-independence side could win. And after two years of debate and disputation, the campaign was suddenly electrified.
It was only one poll and a very narrow lead, but the YouGov findings were in line with the trend of other recent polls showing a surge for Yes.
And if anyone was in any doubt about whether it should be taken seriously, they only needed to look at the No side.
The reaction of Labour, Conservative and Liberal Democrat politicians said more about the importance of the poll than any expert analysis.
The rush to talk about more powers, the “love-bombing” messages from the pro-UK campaigners and yesterday’s unprecedented abandonment of Prime Minister’s Questions so the party leaders could travel north all speak of panic and desperation.
It was almost as if this was the first time the London-based leaders had taken the whole referendum seriously. Despite previous protestations that no-one was being complacent or taking anything for granted, it is now hard to avoid the conclusion that is exactly what they were doing.
Gordon Brown cut a more credible figure when he used a speech in Loanhead to argue the case for sticking with the UK and outline a timetable for delivering more powers.
But the fact remains the three main anti-independence parties are not agreed on what those powers should be. There may be “overlap” and “common ground” between their proposals, but there are also major differences. Labour’s plans – the least radical – only emerged after a bitter fight inside the party so moving from that is not going to be easy.
The hastily-arranged appearance by Johann Lamont, Ruth Davidson and Willie Rennie outside Our Dynamic Earth to endorse the timetable set out by Mr Brown only added to the impression of panic in the No camp.
It seems surprising that political advisers have not worked out that frenetic activity in these circumstances is likely to be counterproductive.
Some of the fear among the anti-independence parties stems from the detail in the polls. They picked up an increase in support for independence among women – the group which seemed most difficult for Alex Salmond and his fellow Yes campaigners to convince.
And they also found the only group with a significant majority still planning to vote No is older people -–prompting Mr Salmond to tell Yes supporters: “This is a great excuse to pop round for Sunday lunch at your gran’s”
So how’s it going to go next Thursday? Time is running out, but there are still undecided voters and people who think they know how they are going to vote but could yet be persuaded.
Will the polls have galvanised No voters to turn out and save the Union? Will those intending to vote Yes have a last-minute change of heart at the polling station? Or will the Yes surge generate even more momentum? Both campaigns are working flat out because, even at this eleventh hour, it looks as if it’s still all to play for.