The Ulster Unionist Party has suffered heavily in the local government elections, losing 39 seats, more than 5 percentage points in popular support and its lead position within unionism.
The Democratic Unionists picked up 39 seats across the North's 26 councils as its advance continued in the wake of dramatic gains in last week's Westminster election.
The Rev Ian Paisley's party now holds 182 seats, eclipsing the Ulster Unionists on 115 and well ahead of Sinn Féin, the second largest party, on 126 councillors. The SDLP won 101 seats, down from the 117 it won at the last local government election in 2001.
DUP councillors won outright control of Castlereagh, Ards and Ballymena councils, is the largest single party in Belfast and made sweeping gains in Lisburn.
Reflecting the crisis within the UUP, David Burnside, the defeated Ulster Unionist MP in South Antrim, warned last night that his party needed major reform if it was to survive.
"The UUP have had presentational and organisational problems for years," he said.
"We cannot afford to cobble together again the same facade as recent years, featuring the same people who have been responsible for our failures."
The SDLP suffered as Sinn Féin made gains, but held on to its largest-party status in both Down and Derry City. Party president Gerry Adams claimed: "This week Sinn Féin has gone from strength to strength. Building on our success in last year's local government elections in the 26 counties, we now have representation for the first time in Ballymena, Banbridge and Coleraine. Our party was returned in even greater numbers in Omagh, Armagh, Dungannon, Magherafelt and Strabane."
However, in a major surprise, the outgoing Sinn Féin mayor of Derry, Gearóid Ó hEára lost his seat to a party colleague.
The Green Party won three seats, prompting party leader Trevor Sargent to claim his party has a strong base on which to base a challenge for an Assembly seat.
Democratic Unionists will be the largest single party in Belfast City Council. The party took 15 seats in the 51-seat chamber, one more than Sinn Féin.
Both parties significantly increased their totals of councillors and enhanced their shares of the popular vote compared to the last local government elections in 2001.
The DUP secured 25.8 per cent of the popular vote, a rise of 7.7 percentage points, largely at the expense of the Ulster Unionists which saw its support slip by 4.5 points and which had its worst local government election in years.
The SDLP lost one councillor and saw its popular vote slip by a fraction in what was otherwise a solid performance.The Alliance Party was buoyed by its performance which saw it pick up one seat in east Belfast including the Short Strand area where the McCartney family lives. Maire Hendron, whose brother-in-law is the former SDLP West Belfast MP, Dr Joe Hendron, took the seat once held by Sinn Féin's Joe O'Donnell who did not seek re-election.
The Alliance's overall share of first preferences in the city rose by nearly one point to 6.8 per cent.
Party leader David Ford said his party had performed well despite the holding of the local government poll on the same day as the Westminster election. He believed this kept a media focus on the largest unionist and nationalist parties at the expense of the smaller parties.
Progressive Unionist leader David Ervine retained his seat in east Belfast as did former leader Hughie Smyth in west Belfast. But party colleague Billy Hutchinson lost his seat in the north of the city.
Frank McCoubrey is now the sole Independent member of the council. Mr McCoubrey is a member of the Ulster Political Research Group which provides political analysis for the Ulster Defence Association.
With the share of seats poised at 22 for Sinn Féin and the SDLP and 24 for the various unionists, Alliance holds the balance and has sufficient seats to determine the destiny of the Lord Mayor's chain if the two political blocs oppose each other. The DUP tally of seats could have been higher had it run additional candidates.
Diane Dodds, whose husband is North Belfast MP Nigel Dodds, won 3.5 quotas in the Court ward of west Belfast and brought in two party colleagues. Had the party run another candidate, another seat could have been taken. The party is also claiming the election of the youngest candidate to the city council.
Christopher Stalford (22), first-time candidate, won a seat in the Laganbank ward which includes the solidly loyalist Donegall Pass and Sandy Row areas.