Sinn Féin leader Mary Lou McDonald faces another headache as her party's Border region European Election candidate admitted he is in a desperate battle to keep his seat.
att Carthy assessed his chances of staying in Brussels saying: "In realistic terms, we're going to be fighting for the last seat."
With counting in Castlebar expected to last until tomorrow and possibly Thursday he said it could come down to "the smallest of margins".
Sitting Fine Gael MEP Mairead McGuinness stormed to victory in Midlands-North-West, topping the poll and being elected on the first count with a huge vote of 134,630.
Her running mate, former Rose of Tralee Maria Walsh, was on 64,500 votes and in with a shot of taking a second seat for Fine Gael. Such a result would be one of the few positives from a lacklustre election season for Taoiseach Leo Varadkar.
Ms Walsh got a boost of just over 6,000 transfers from Ms McGuinness in the second count, bringing her to 70,536.
Independent Luke 'Ming' Flanagan is in a stronger position to hold on to his seat as he came second in the first count with a vote of 85,034. And there is a furious scrap for the fourth seat with Mr Carthy, controversial ex-presidential candidate Peter Casey, and the Green Party's Saoirse McHugh all still in contention.
Ms McHugh's prospect of election diminished as her 51,019 first preference result fell short of her predicted support in the RTÉ exit poll. Last night she said she was "overwhelmed" at the vote she got but said: "I'm not expecting to get a seat."
Sinn Féin, meanwhile, has had a dismal showing in the local elections and its European seats in Midlands-North-West and Dublin are at risk. Mr Carthy conceded that the party will be "in trouble" if the performance is replicated in the next general election.
He got 77,619 first preferences, but he said he is in a "battle for transfers" and is "more hopeful than confident" he will be in the mix for the final seat.
Fianna Fáil's two-candidate strategy in the constituency failed for the second European Election in a row. Cavan-Monaghan TD Brendan Smith, who got 42,814 first preferences, said the party will examine what went wrong when the count is over. He effectively conceded he won't win a seat.