Left-wing ex-Education Minister Benoit Hamon and ex-PM Manuel Valls will contest a run-off to become the Socialist candidate in France’s presidential election in April.
It was clear the pair would advance from a field of seven after half the votes were counted in Sunday’s primary.
The run-off will be held next Sunday.
Opinion polls suggest that whoever wins will have little chance of reaching the final round of the presidential election in May.
With half of the votes counted, Hamon, 48, who was sacked by the government of President Francois Hollande, was ahead on 36.1%, with centrist Valls, 54, on 31.2%.
Another left-winger, Arnaud Montebourg, was in third place.
But the extent of the top pair’s lead ensured they would not be caught.
Valls said the choice in the second round would be “between an assured defeat and possible victory”.
Hamon said voters had sent “a clear message of hope and revival and a desire to turn a new page in the history of the Left and of France”.
Source: BBC