French Socialist leaders Francois Hollande and Martine Aubry, bitter rivals despite coming from the same wing of their party, face a tight battle for the right to run against Nicolas Sarkozy last year.
Hollande took the lead over Aubry in the first round of primary voting on Sunday, but at 39 to 31 percent, their scores were close enough that she has a chance to outflank him on the left and grab the nomination in the run-off.
The stakes are high - opinion polls suggest either Socialist would beat the centre-right incumbent in next April's presidential election - and the pair have a history of enmity despite their similar political outlooks.
Hollande was still predicting victory, but admitted he does not expect a "very wide I'm campaigning for fundamental change and... I'll beat Sarkozy in 2012."
They are from the same generation; he is 57 and she 61. Both were acolytes of former European Commission chairman Jacques Delors: Aubry is his daughter, Hollande led the backroom team that urged him to run for president in 1995.
Delors demurred, and the left has been excluded from the presidency ever since. During this time, Hollande and Aubry's careers diverged.
She is mayor of Lille and, as labour minister and number two cabinet figure under Socialist premier Lionel Jospin, introduced France's 35-hour working week. He was leader of the party, but has never held high office.
Both remain on the ideological centre ground within the party, but Aubry tacked to the left -- at least rhetorically -- during the primary campaign, rallying the party's base in a time of austerity and economic crisis.
Hollande is now under pressure to do the same. The third placed candidate in the first round of the primary was Arnaud Montebourg, who campaigned on a platform of protectionism and tougher controls on financial markets.
The candidate who wins on Sunday will be the one who convinces those on the left of the party that he or she offers a better chance of a clean break with Sarkozy and the right's austere economic programme.
Montebourg has not yet thrown his weight between either frontrunner, but most observers expect the bulk of his voters to lean towards Aubry.
"You can't fight the hard right with the soft left," Aubry declared ahead of the primary, and no one was in any doubt about whom she meant.
When Aubry replaced Hollande as Socialist leader in 2008 she was fiercely critical of his collegial, easy-going style of leadership, which she felt had left the party rudderless and divided into warring factions.
She let it be known she wasn't impressed by the allegedly dilapidated condition of party headquarters, and aides mocked Hollande's jovial public persona, joking on television chatshows while Aubry pushed policy.
Hollande responded with a presidential make-over, toning down his humour, adopting a more serious tone and shedding 10 kilos of body fat. He built a strong lead in opinion polls but never quite shook off the chasing pack.
The right had been hoping that the US-style open primary, a political novelty in France, would trigger a bout of the infighting that has blighted Socialist prospects so often in recent years.
Read more of this story from AFP.