Sinn Féin's vote surge continued in the Laois-Offaly constituency when its candidate Brian Stanley was elected on the first count with a surplus of 5,083 votes.
Speaking after his election, Mr Stanley said his first preferred option on the formation of the next administration “would be to form a left-wing government”.
“My second preference would be to form as close to a left-wing government as possible,” he said.
The count in Portlaoise has been adjourned for the night after the third count, with just Mr Stanley elected. It will resume in the morning at 9am.
The reason why the Fianna Fáil vote was not as expected, according to party TD Seán Fleming, was because his party was "seen as too close to Fine Gael in government for the past four years".
Mr Fleming said: “The confidence-and-supply agreement between Fine Gael and Fianna Fáil was the right decision for the first year or so, to give the country stability, but it went on for far too long.”
However, Fianna Fáil is still on track to secure the two seats it held in the five-seat constituency, with Mr Fleming and Barry Cowen expected to be elected. Fine Gael's Charlie Flanagan is also anticipated to retain his seat.
The fifth and final seat will be a close affair between the outgoing Independent TD Carol Nolan and Fianna Fáil's Peter Ormond.
Candidates: Marcella Corcoran-Kennedy (FG), Charlie Flanagan (FG), Barry Cowen (FF), Seán Fleming (FF), Peter Ormond (FF), Pauline Flanagan (FF), Brian Stanley (SF), Pippa Hackett (GP), Stephen Tynan (PBP), Ken Smollen (Irish Democratic Party), John Daly (National Party), Carol Nolan (Ind), John Leahy (Ind), Noel O'Rourke (Renua), Noel Tuohy (Lab).