Francois Hollande took a step closer to becoming the next president of France after beating Nicolas Sarkozy in the first round of voting, but Marine Le Pen could act as kingmaker after a strong result from her National Front party.
The Socialist Party's Hollande received 28.6% of the vote, narrowly beating President Sarkozy, but Le Pen caused the biggest shock of the evening by surging to 18%, the biggest result for a far-right candidate.
French election results:
"The battle of France has only just begun," Le Pen, daughter of National Front founder Jean-Marie Le Pen, told supporters. She is set to give her opinion on the run-off during a May Day rally in Paris next week.
The French president challenged Hollande to a series of three debates in the run-up to the final vote. Socialist aides said Hollande, who is a less accomplished television performer than Sarkozy, would only accept one debate on May 2.
If he loses the election, the French president will join 10 other eurozone leaders who have been ousted from office since the crisis started in late 2009.
Political pundits said Hollande appeared to have larger reserves of second-round votes than Sarkozy, who would need to pick up at least three quarters of Le Pen's supporters and two thirds of Bayrou's to gain victory.
Polls taken on Sunday by three institutes suggested that between 48% and 60% of Le Pen voters planned to switch to the president, while Bayrou's backers split almost evenly between the two finalists, with one third undecided.
If elected, Hollande, who is aiming to become the first Socialist president in 17 years, will impose a 75% tax on the wealthiest - those earning over a million Euros - and is aiming to create growth in the eurozone.