By Pierre Savary and Nicholas Vinocur
HENIN-BEAUMONT, France (Reuters) - French far-right leader Marine Le Pen took a commanding lead in the first round of a legislative election on Sunday, raising the prospect of a seat in parliament for her anti-immigrant party as her arch-foe, firebrand leftist Jean-Luc Melenchon, bowed out.
Le Pen won more than 42 percent of the vote in a working class district in northern France where she has established a loyal base for the National Front, tapping into unease over high unemployment and years of economic decline.
She faces a close-fought run-off next Sunday against a Socialist who should pick up votes from Melenchon supporters.
But, buoyed by deep-running anger over an economic crisis many see caused by the euro zone, her anti-euro party is at its closest in years to winning seats in parliament, making it to the run-off in four constituencies across France.
Le Pen, a dynamic 43-year-old, said the result in and around the former coal-mining town of Henin-Beaumont showed that her party remained a powerful political force after she placed came in the first round of this year's presidential election.
"Tonight, we confirm our position as the third political force in France," she said in front of cheering supporters.
The first-round election left President Francois Hollande on track for a Socialist-led majority in parliament after a solid win that should free him from having to rely on hard leftists or opposition conservatives to govern.
The local battle between Le Pen and Left Front coalition leader Jean-Luc Melenchon gripped France as the two outsize personalities faced off in a scarred landscape of run-down miners' houses, towering slag heaps and economic despair.
While they had promised to compete in a civil manner, the campaign turned nasty last week as Melenchon accused Le Pen of dirty tricks, notably distributing political tracts depicting him in Nazi garb or featuring messages in Arabic script.
Le Pen will face Socialist Party candidate Philippe Kemel, who came in second place with 23.5 percent of votes, according to an official tally, in a final runoff on June 17.
If she, or other National Front candidates in three other constituencies, wins the National Front would take a seat in the lower house National Assembly for the first time since 1986.
Melenchon, who got 21.48 percent of votes in Henin-Beaumont, conceded defeat in a brief speech under driving rain, saying his party had made progress but not enough to beat Kemel.
"I'm afraid you might be a bit disappointed," he told a silent crowd of supporters, adding that the second round would be very difficult for Le Pen, despite her high score.
The defeat robs the powerful orator, who came fourth in the first presidential round in late April and drew huge crowds to open-air rallies with fist-shaking speeches aiming to revive France's revolutionary spirit, of a platform in parliament.
Among the other constituencies where the far-right did well, Le Pen's 22-year-old niece, Marion Marechal-Le Pen, placed first in a southern district where she will compete with a Socialist and a centre-right candidate in a three-way final round.
Elsewhere, party spokesman Florian Philippot was due for a duel with a Socialist in eastern France and Gilbert Collard, a prominent lawyer and recent National Front member, came first in the southern Camargue district.
(Reporting By Pierre Savary, writing by Nicholas Vinocur; Editing by Paul Taylor and Jon Hemming)