By Richard Balmforth | PARIS

French centrist Emmanuel Macron and far-right leader Marine Le Pen clung on as frontrunners in France’s tight presidential race on Tuesday, but the unpredictable outcome is pushing some pollsters to calculate the most extreme runoff scenarios.

In a new twist in the two-round election, Jean-Luc Melenchon, a far-left veteran who for most of the campaign has been dismissed as a distant no-hoper, has surged into the top four and lies just a few percentage points behind the leaders.

Though some commentators see Melenchon’s challenge as a blip that may fade, his rise has injected further uncertainty into the outcome of the race for the Elysee, in which Macron has largely been seen as the favorite.

http://www.reuters.com/article/us-france-election-idUSKBN17D18R