French Socialist leaders Francois Hollande and Martine Aubry face off in a final debate Wednesday amid an increasingly bitter battle for the right to run against Nicolas Sarkozy next year.
Hollande took the lead over Aubry in the first round of primary voting this week 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 Sunday's run-off.
The stakes are high -- opinion polls suggest either Socialist would beat centre-right incumbent Sarkozy in next April's presidential election.
The tone of the battle has hardened ahead of the debate, with Aubry hitting out at Hollande's alleged centrist tendancies.
"I have said what I want to do, and it's the opposite of the soft left," Aubry, the 61-year-old mayor of Lille, said this week.
Hollande, a 57-year-old former Socialist party leader, in turn accused his rival of "insidious" attacks and "underhanded manoeuvres".
With the war of words escalating, a spokesman for organisers of the Socialist primary, Jean-Pierre Mignard, warned the two candidates against "denigration" and "bickering".
The debate, which will air on national television from 8:35 pm (1835 GMT), will see the two rivals answering questions on the economic crisis, social issues and foreign affairs from a panel of journalists.
Among those watching the debate will be two defeated candidates from Sunday's primary, Arnaud Montebourg, who took 17 percent with a protectionist campaign urging tougher controls on financial markets, and former presidential candidate Segolene Royal, who took seven percent.
Both have yet to back either of the remaining candidates.
Hollande has won the support of the last placed candidates from Sunday's first round, lawmakers Manuel Valls and Jean-Michel Baylet, both seen as being on the right-wing of the left.
A public opinion poll by firm OpinionWay-Fiducial for newspaper Le Figaro released Tuesday showed Hollande in the lead with 54 percent support against Aubry's 46 percent.
Both Hollande and Aubry hail from the ideological centre ground within the party, but Aubry tacked to the left during the primary campaign, rallying the party's base in a time of austerity and economic crisis.
The US-style open primary, a political novelty in France, has proven popular and given a boost to Socialist hopes to use the energy generated by the race as a springboard for the presidential elections.
More than 2.5 million voters turned out for Sunday's first-round vote and more than 4.9 million watched the first primary debate in mid-September.