The leader of Fianna Fail has failed to rule out entering government with Sinn Fein in the Republic after a general election that's set to transform the political landscape.
As video emerged of a triumphant Sinn Fein TD Dessie Ellis and supporters singing rebel song Come Out Ye Black And Tans at the election count in the RDS, unionists expressed their concerns about the prospect of Sinn Fein being in government on both sides of the border.
Sinn Fein is set to significantly increase its number of seats in the Dail after it topped the polls across the country when first preferences were added up.
Arriving at his count centre in Cork, Fianna Fail leader Micheal Martin would not rule out working with Sinn Fein or Fine Gael, having definitively refused to countenance either as coalition partners during the campaign.
Mr Martin, who said his party looked like being on course to win the most seats, was repeatedly pressed to restate his opposition to a potential Sinn Fein partnership.
While insisting there were "significant incompatibility" issues in terms of policy, he did not dismiss the suggestion outright.
"Our policies, our positions and principles haven't changed overnight or in 24 hours," he said.
"It's very daunting, to say the least. It's only a few months ago that they were trailing in the polls," he said. "What has changed? What has caused the surge in Sinn Fein support? I don't understand it.
"Flabbergasted would be the word.
"I think Sinn Fein is the only party that, no matter what they do, it does them no harm.
"It's very worrying, from a unionist point of view, they there are getting the level of support that they are getting," Mr Worton said.
Ulster Unionist leader Steve Aiken felt it heralded a worrying time for residents of the Republic.
"The results of yesterday's election in the Irish Republic show a fracturing of the traditional FF/FG 'duopoly'," he said.
"That there appears to be no party large enough to command the support for a majority government will face the Irish electorate with the choice between another, potentially inconclusive election, or a coalition government between a centre-Right party, heavily leaning on international banking and foreign direct investment from USA, and a hard-Left party, with a less than transparent relationship with its violent past, and whose economic and social policy influences are those of Venezuela and Cuba.
"Our neighbours are living in interesting, if worrying, times."
TUV leader Jim Allister said the Sinn Fein advance should give unionist leaders "cause for thought".
"In the Republic's election Leo Varadkar is reaping what he sowed," he said.
"By insisting Sinn Fein was fit for government in Northern Ireland, and must be included, he validated and sanitised the party of the IRA.
"Likewise, by the DUP making Sinn Fein's elevation into Stormont government possible, they short-sightedly endorsed them as a party fit for government. Now Ireland, north and south, is blighted with their growth. 'Moving forward', wasn't that the DUP slogan?
"Sadly, it is those they partnered into government that are on the move, singing IRA songs. The correlation is obvious.
"The only comfort is that a triumphalist Sinn Fein in the Republic gives unionists even more reason to be opposed to an all-Ireland, but it should give the lead party of unionism cause for thought."
A DUP spokesman said on Sunday night: "We note the election results so far in the Republic of Ireland.
"When a government is formed, we will work constructively with it on matters of mutual concern."
Former Sinn Fein leader Gerry Adams said Irish voters have registered a "step change" in politics. Speaking to RTE, Mr Adams said: "There has been a realignment of politics across this island."