The poll, conducted between between April 28 and May 3, also found support for a second referendum on Scottish independence had fallen since last month, as had the First Minister’s approval rating.
In the constituency vote, support for the SNP was at 51 per cent, a drop of two points from the previous poll in April, with both the Tories and Labour making gains.
Douglas Ross’s Scottish Conservatives were up two points to 23 per cent, with Labour up by one point to 19 per cent.
An outright majority
On the regional ballot, SNP support dropped by three points to 41 per cent, with the Tories up by one point to 23 per cent and Labour remaining steady on 17 per cent.
Support for the Liberal Democrats was at 7 per cent in the constituency section of the ballot and 6 per cent on the regional list.
Meanwhile, 8 per cent of voters said they would back the Scottish Greens on the list – and another 3 per cent said they planned to vote for Alex Salmond’s Alba Party.
Despite the fall in its support, seat projections based on Opinium’s polling suggest the SNP could still win an outright majority in Holyrood.
The party would be able to rule without the help of its former coalition partners, the Scottish Greens, with 67 of the 129 seats in the Scottish Parliament.
The Tories are forecast to hold onto second place with 29 MSPs – ahead of Anas Sarwar’s party on 20.
On the key issue of Scottish independence, the 1,015 voters surveyed were split 50:50 when “don’t knows” are removed – down from 51 per cent support for Yes in last month’s poll.
Less than three out of ten (28 per cent) of those questioned wanted a referendum in the next two years, with support for a second independence vote in this timescale down by five points on the previous study.
Meanwhile, a further 14 per cent of voters think a fresh vote on independence should happen in the next two to five years, a drop of two points.
By contrast, half (50 per cent) of those surveyed did not want a referendum within the next five years.
In more positive news for Ms Sturgeon, the poll found she was still the most popular of the party leaders in Scotland, with a net approval rating of +17 - thought that figure is down from +23 last month.
By contrast, Mr Sarwar has seen his approval rating continue to grow, from +10 in April to +13.
Mr Ross has a rating of -26, although this is up from -31 the previous month. Mr Salmond is the least popular of the leaders, with a net approval rating of -70.
Chris Curtis, senior research manager at Opinium, said: “The campaign finishes much where it started, with razor-thin margins set to decide whether Nicola Sturgeon can govern alone or will need the backing of other pro-independence parties.”
“Our latest polling shows the Scottish public are not necessarily keen on another Scottish independence referendum.”
He said that even if Ms Sturgeon did succeed in winning a majority, just 43 per cent of people want another referendum in the next five years, compared to 50 per cent who are opposed to this.
Mr Curtis said: “We have also seen Labour voters harden in their view over the campaign, with just 24 per cent willing to back one in those circumstances.
“Regardless, Sturgeon will argue that a good result this week gives her the mandate to put the question back to the Scottish people, demonstrating just how important this week’s vote will be for the future of the Union.”
‘The outcome is on a knife edge’
Commenting on the Sky News poll, SNP depute leader Keith Brown said: “If you want the experienced leadership of Nicola Sturgeon to get us through the pandemic and into recovery, then it has to be both votes SNP on Thursday.
“Every vote counts in this election. The outcome is on a knife edge and Labour and the Tories are teaming up to try and stop Scotland making progress.
He added: “Anything less than both votes for the SNP risks leaving Scotland’s future in the hands of Boris Johnson and the Tories instead of the safe hands of Nicola Sturgeon.”
At the same time, Labour’s shadow Scotland secretary Ian Murray said: “Getting our NHS, education, jobs, climate, and communities back on their feet should be the Parliament’s priority.
“Division only distracts from the real life concerns of you and your family and forces our national recovery to take a back seat.
“If you agree your parliament’s focus should be on recovery, use both your votes, especially the peach ballot paper, for Anas Sarwar’s Scottish Labour.”
Pamela Nash, chief executive of the pro-union campaign group Scotland in Union, said: “This is a clear message for Nicola Sturgeon – whatever wild claims she makes about the election result, the people of Scotland do not support her timetable for another divisive referendum by 2023.
“The priorities of the people of Scotland are jobs, health and the environment – not more division.
“On Thursday, people should vote for Scotland’s priorities, not the SNP’s priorities.”