Should President Nicolas Sarkozy lose on Monday, he would become France's first head of state in 31 years to be booted out after a single term.
Running what so far has been a masterly campaign, the placid Socialist challenger Francois Hollande is favoured with between 53 and 55 per cent of the vote, against 45-47 per cent for the temperamental President.
But Sarkozy is one of France's toughest politicians, and never better than when his back is to the wall.
"He says it's still winnable. We can get in by a whisker," said a source in Sarkozy's conservative Union for a Popular Majority (UMP).
If Sarkozy wins over a large slice of far-right and undecided voters and if there is a strong turnout, he would scrape together enough for a win, according to this strategy.
All eyes will be on far-right National Front leader Marine Le Pen, who is still to announce whether she will back either candidate. But her support for Sarkozy looks as remote as it does for Hollande. She accuses Sarkozy of hijacking her ideas on immigration, security and national borders.
Sarkozy believes a one-on-one TV debate on Thursday will give him the chance to deliver a knockout blow before tens of millions of voters.
Christian Delporte, author of a book on TV debates, says it will be "a great spectacle" but is unsure if it will change minds.
"It's the incumbent president who is in the role of challenger. This is a first," said Delporte. "He is going to have come out on the offensive but not be aggressive. Francois Hollande, on the other hand, will have to show that he can ride out the blows but not be a punchbag."
Hollande's Achilles' heel has been his demand to renegotiate the fiscal pact Sarkozy laboriously crafted with German Chancellor Angela Merkel to save the euro with a cast-iron set of budget rules.
But Hollande last week confounded his critics by spelling out only moderate changes, all aimed at spurring growth. His plan sees the floating of infrastructure bonds by the European Investment Bank. It would not see issuing of bonds by the European Central Bank - an idea Germany furiously opposes as it would mean pooling national debts in the 17 eurozone countries.
The scheme gained early murmurs of approval from European policymakers who fear the "Merkozy" austerity-only approach might sink the entire eurozone.
Merkel, meanwhile, who has never developed a liking for Sarkozy, stressed she could work with any French president.
Sarkozy's lieutenants have been vigilant about maintaining unity in the final days. But with Hollande seemingly unbeatable, the first shots have been fired in the post-election battle for the UMP's soul.
Centrists such as former ecology and sports minister Chantal Jouanno have deplored the obsession with wooing the National Front vote. They fear the UMP will be consigned to the wilderness in a landscape dominated by the broad left and a popular far right.By Catherine Field Email Catherine