Lance Armstrong retained the overall lead but lost a key teammate in a crash as the Tour de France headed out of the Alps in a stage won by David Moncoutie on Bastille Day.

Moncoutie became the 15th Frenchman since World War II to win on France's national holiday. It was his second stage win in five Tours.

"It's fabulous," Moncoutie said. "I'm so happy to win. It's July 14th."

Moncoutie took the lead on the Col du Corobin, the fourth of five ascents on the 187-kilometre trek from Briancon to Digne-les-Bains, and cycled alone to the finish past cheering crowds. The Cofidis team rider completed the 12th stage in 4 hours, 20 minutes, 6 seconds.

Armstrong cruised in with his main rivals in a group more than 10 minutes back, but he lost teammate Manuel Beltran, who crashed and abandoned the race.

The Spanish rider, known as "Triki" by his teammates, fell on the Cote des Demoiselles Coiffees climb, the stage's first ascent.

He got back on his bike but later quit on the advice of a Tour doctor. He was being kept overnight for observation at a hospital, although initial examinations found no serious injury.

Beltran, 34, is a specialist mountain climber and will be missed by Armstrong when the race heads into the Pyrenees on Saturday. He has been part of the American's Tour-winning team since 2003.

"It could be very critical with the days that we have coming up," Armstrong said. "Three tough days in the Pyrenees. We don't want to lose any climbers and Triki is one of our pure climbers."

But Armstrong said he felt that he could rely on his remaining seven Discovery Channel teammates to help fill Beltran's place in the mountains that straddle France and Spain.

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