Lance Armstrong easily retained his overall lead in a tricky stage 18 of the Tour de France, won by Marcos Serrano of Spain.

Armstrong finished in a group of four with Ivan Basso of Italy, Jan Ullrich of Germany and Cadel Evans of Australia.

They broke away from other riders with violent bursts of speed up a brutal final ascent at Mende, in south-central France.

Armstrong's lead over Basso remained unchanged at 2 minutes, 46 seconds.

Third-placed Mickael Rasmussen was slower up the last climb and slipped to 3:46 behind the record six-time champion.

Ullrich was still fourth, 5:58 behind Armstrong, but closed on Rasmussen.

The 1997 Tour winner improved his chances of overtaking the Dane in the time trial on Saturday, the penultimate day of the three-week race.

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