Sinn Fein has taken the Newry and Armagh seat from the SDLP. Conor Murphy defeated its candidate, Dominic Bradley, by 20,965 votes to 12,770.
Conor Murphy wins Newry and Armagh for Sinn Fein
The seat had been held by former SDLP deputy leader Seamus Mallon who stepped down this time.
The defeat is softened by an SDLP gain in South Belfast for Alasdair McDonnell and the success of party leader Mark Durkan in Foyle.
Sinn Fein has finished in the election with a total of five seats.
The SDLP's candidate Dominic Bradley is a former teacher with strong GAA connections.
But there were clues about how he might do from his performance in the Assembly election of 2003 when his first preference vote was about half the size of Conor Murphy's.
The gap between the two parties had begun to narrow in 2001 when Sinn Fein trailed the SDLP by only 6%.
This was a rise of 10% on the 1997 result.
The DUP's Paul Berry was in third place in Friday's poll with 9,311 votes.