Vote 2011: Plaid deputy Helen Mary Jones loses Llanelli
Labour have taken the key seat of Llanelli from Plaid Cymru, defeating the party's deputy leader Helen Mary Jones.
Keith Davies had just an 80 majority over Ms Jones after a recount in the Carmarthenshire constituency.
Ms Jones has been a member of the assembly since it was formed in 1999.
In the closest Welsh result of the night so far, Mr Davies polled 10,359 - 39.74% of the votes, to Ms Jones' 10,279.
Mr Davies, who is in his 70s, welcomed his election, saying: "I am a Welsh man, I am a socialist. I'm looking forward to working hard for Wales and Llanelli in the National Assembly."
Ms Jones conceded: "We had to swim against a strong tide, we swam hard, we swam well. It wasn't quite enough to bring us home this time."
She said: "We have been in this place before in this hall, and had come back. We will again."
Former prominent Plaid Cymru campaigner Sian Caiach, standing as an independent, polled over 2,000 votes in the constituency.
Plaid Cymru MP Jonathan Edwards said it was a big loss to the assembly. He said he was surprised at the amount of votes that Ms Caiach had polled.
Before the result was announced, Ms Jones said the party had been received positively on the doorstep but that they had faced "a strong national swing towards Labour".
Ms Jones, 50, has been one of the most recognisable assembly AMs and was a longtime health spokeswoman for her party.
She was a former contender for the Plaid Cymru leadership.
Party leader Ieuan Wyn Jones said: "I have no doubt that Helen will once again play a very important role in shaping the future of Wales".
In another blow to the party, former Plaid AM Nerys Evans failed to win Carmarthen West and South Pembrokeshire, after contesting the constituency rather than a list seat, which was held by the Conservatives.
Across the rest of the region there have been few surprises.
The Conservatives also held Preseli Pembrokeshire, while Plaid held Carmarthen East & Dinefwr.
Meanwhile, Health Minister Edwina Hart has retained Gower for Labour as did Gwenda Thomas in Neath and David Felix-Rees in Aberavon.
The four South Wales West regional AMs are: Suzy Davies (Welsh Conservatives), Bethan Jenkins (Plaid Cymru), Byron Davies (Welsh Conservatives), Peter Black (Liberal Democrats).
Plaid's health spokesman and GP, Dr Dai Lloyd, lost his seat due to a Tory gain.