Lance Armstrong prepared for his final push to Paris by taking it easy with the main bunch, letting Spaniard Juan Miguel Mercado have his moment of glory on the Tour de France's 18th stage.

Mercado outsprinted compatriot Jose Vicente Garcia Acosta on Friday to win the 166.5-km stage across the Jura mountains, with Kazakh Dmitri Fofonov leading the rest of a six-man breakaway group to cross the line 11 seconds later in third place.

Armstrong, who finished in the main pack, 11 minutes and 29 seconds behind Mercado, retained his overall lead of 4:09 over Italian Ivan Basso.

Two days before a likely record sixth Tour victory, Armstrong had early on Friday displayed a show of strength following his three consecutive stage wins in the Alps, breaking away from the main bunch to chase the leaders.

The American had attacked behind Italian Filippo Simeoni, who had surged ahead in a bid to catch the six leaders.

Simeoni is one of the American's most bitter rivals off the bike. The two are involved in a legal battle with the Italian suing Armstrong for defamation.

But Garcia Acosta spoke to Armstrong, asking him to do the six a favour and leave them to fight for victory. Armstrong accepted, but only if Simeoni left the break as well.

The stage ended in relaxed fashion until the last 10 kilometres, when Garcia Acosta and Mercado broke clear of their group to go for victory.

Mercado outwitted his older compatriot in the final stretch to give his Quick Step team their third stage victory in this Tour.

Armstrong is expected to increase his overall lead in Saturday's 55-km individual time trial in Besancon.