In the biggest scalp of the night so far, DUP Westminster leader Nigel Dodds – whose party propped up Theresa May’s administration – lost his Belfast North seat to Sinn Fein.
John Finucane took the seat, which Mr Dodds had held since 2001, in what is a huge blow for the unionist party.
Mr Finucane took 23,078 votes over Mr Dodds' 21,135.
After the result, Mr Dodds said: “Boris Johnson we must have a Brexit that ensures it protects the integrity of the United Kingdom.”
Mr Dodds has been very prominent for the DUP during Brexit negotiations.
DUP leader Arlene Foster said it was a “hugely disappointing” evening for her party.
“It was very clear in both North Belfast and South Belfast that nationalism came together and decided they were going to get rid of Emma (Little-Pengelly) and Nigel (Dodds).
“We fought very hard aganst that but the numbers were against us in both constituencies.”
She rejected any suggestion the vote called into question her leadership.
“If you look at the votes you will find the greater number of people in Northern Ireland still want to remain within the UK.
“That to me is a very important point.”
It came after the deputy leader of the Alliance Party Stephen Farry cruised to victory with a majority of almost 3,000 votes in the affluent Belfast commuter constituency of North Down.
Mr Farry’s victory provides further evidence of the so-called Alliance surge, coming as it does after a series of positive elections for the middle-ground cross-community party.
The result landed another blow to the DUP on what has shaped up to be a very disappointing election for the unionist party.
The DUP is vehemently opposed to Mr Johnson’s Brexit deal, claiming it will create economic borders down the Irish Sea and weakened Northern Ireland’s place within the Union.
Long-standing DUP MP Sammy Wilson, who is on course to retain his East Antrim seat, insisted his party could still secure changes to the agreement despite the predicted Tory majority.
“Obviously we’d have preferred to be in a situation we were in the last Parliament where we did have the influence and where it was fairly marginal, however for the country it probably wasn’t a great thing because no decisions could be made,” he said.
“I still wouldn’t be totally dismayed insofar as a big majority could actually mean that Boris Johnson can go in and be fairly bullish with the EU when it comes to negotiations, and if he does do that then many of the problems the current deal is going to cause Northern Ireland could disappear.”
The election comes ahead of the latest bid to resurrect the crisis-hit institutions at Stormont.
Ahead of an anticipated round of negotiations on Monday, Sinn Fein vice president Michelle O’Neill said: “Whatever the results, Sinn Fein will be in the talks on Monday morning to work to secure a genuine power-sharing executive which is credible and sustainable to deliver good government and properly resourced public services to all.
“Sinn Fein will continue to represent people where it matters and stand up against Brexit.”
