The seat in the General Election has gone to Joan Burton, the Labour Party finance spokeswoman.
The Dublin West TD topped the poll with 9,627 votes in a constituency where Finance Minister Brian Lenihan is fighting for political survival.
The Fianna Fail candidate is battling to take the third seat with his party mired in its worst electoral performance in history.
Ms Burton said: "Labour has had a very good day."
Mr Lenihan is in a battle for the two remaining seats in Dublin West with Leo Varadkar of Fine Gael and Socialist Party MEP Joe Higgins.
Ms Burton said she expected a large number of seats to go down to the wire late tomorrow.
"I think there will be a large number of nail-biting final seat counts. I think we will all have our fingers chewed down by this time tomorrow," she said.
"I think it's too close to call in a lot of constituencies."