The poll was called after the refusal of the DUP to allow the co-option of a UUP replacement into the Banbridge Council seat left vacant by the resignation of Tyrone Howe.
The count in Dromore bowling pavilion provided high drama with the final result in doubt up until the last few minutes.
The UUP's Carol Black retained the seat for the party, after the electoral debut of the Traditional Unionist Voice slashed the DUP's majority.
After first preference votes were tallied, the DUP's Paul Stewart polled 1,069 voted ahead of Ms Black on 912 and the TUV's Keith Harbinson on 739.
The Alliance Party's David Griffin also produced one of his party's best results in recent years with 357 first preference votes, while Sinn Fein's Paul Gribben polled 350 votes, John Drake of the SDLP 290 and Helen Corry of the Green Party 59 votes.
Transfers from the TUV's Keith Harbinson saw Ms Black clinch victory by 66 votes, her final tally of 1,571 to Stewart's 1,505.
Speaking after the final results were announced Ms Black said she was 'absolutely delighted' for the Ulster Unionist Party.
"We have fought the most fantastic campaign. We had young woman and young men out canvassing and I would like to thank everybody for their hard work," she stated.
She also extended thanks to the deputy returning officer and his staff, the voters of Dromore and district, the other candidates and her election agent Bill Bingham.
"This is absolutely wonderful news for the Ulster Unionist Party," she added.
A disappointed Paul Stewart congratulated Ms Black on her win.
"We have fought a good election," he said extending his thanks to his campaign team.
"Our party will listen to this result and will reflect unlike other parties that didn't take heed of the unionist voice in their communities.
"We are still the largest party in Northern Ireland. We will continue to deliver for the Unionist people. The people of Northern Ireland will see the benefits of devolved government."
Mr Stewart predicted the DUP would go 'from strength to strength'.