Outsider Benoit Hamon will fight former Prime Minister Manuel Valls for the French Socialist party presidential nomination after both made it through the first round of the primary Sunday, partial results showed.
Hamon, former education minister, scored just over 35 percent to 31 percent for Valls as ex-economy minister, while Arnaud Montebourg was eliminated with 18 percent, according to results from one-third of polling stations.
Whoever wins next Sunday's runoff faces long odds as polls currently show the presidential election in April and May shaping up as a three-way contest between conservative ex-premier Francois Fillon, far-right leader Marine Le Pen and Emmanuel Macron, the former economy minister and former bank executive at Rothschild.
Valls, who was slapped this week by a protester, appears to have paid the price for his neoliberal policies as the Socialist government's prime minister and has struggled at times in a campaign he was expected to dominate. His rivals accused him of betraying leftist ideals by forcing through labor market reforms.
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Following his elimination, Montebourg immediately threw his weight behind his former Cabinet colleague Hamon, both of whom represent the Socialists' left flank.
"We left the government together, we fought together. Next Sunday I'll be voting Hamon," Montebourg said.
Hamon performed strongly in three TV debates packed into a short campaign, attracting attention with his proposal to pay the poor and 18- to 25-year-olds a "universal income" rising from 600 euros to 750 euros (US$640 to US$800) a month.
Turnout for the Socialist primary was around half of that of the center-right Republicans primary in November. Between 1.7 million and 1.9 million voted, according to an estimate by the Elabe polling group, compared with the 4 million who took part in the first round of the right-wing primary.
Some Socialist heavyweights have hinted they could support neoliberal social-democrat Macron over their party's nominee, arguing he may have a better chance of reaching the second round of the presidential election against Le Pen.
Macron himself has ruled out a pact with the Socialists, announcing Thursday that his En Marche movement would field hundreds of candidates in parliamentary elections in June.
Communist-backed firebrand Jean-Luc Melenchon, who like Macron is polling in double digits in his campaign as an independent, also risks splitting the left-wing vote. Commenting on the results, he said the Socialist nominee chosen during the runoff vote next Sunday will likely withdraw in favor of Macron or himself, in order to avoid divisions within the left.