Lance Armstrong handed his Tour de France leader's yellow jersey to French champion Thomas Voeckler but could have lost much more in a rainy, windswept 200.5-km fifth stage from Amiens.

Voeckler, who became French champion the week before the Tour on his 25th birthday, was part of a five-man breakaway which reached Chartres with a 12-minute lead over the main bunch that included Armstrong, the five times Tour champion.

Thursday's stage was won by Australian sprinter Stuart O'Grady, who surged to beat Dane Jakob Piil, France's Sandy Casar and Voeckler at the line.

Overall, Voeckler leads O'Grady by three minutes and 13 seconds with Casar third 4:06 behind.

Armstrong, who took the overall lead thanks to a great US Postal effort in Wednesday's team time trial, had said he would not defend his yellow jersey so early in the Tour.

The Texan finished the day sixth in the overall rankings 9:35 adrift of Voeckler.

"We're comfortable with that situation," said Armstrong's team director Johan Bruyneel. "We said we would let breakaways take place and to have the French champion wearing the yellow jersey is ideal.

"We're sure his Brioches La Boulangere team will defend it and it will take pressure off our shoulders."

Voeckler's team chief Jean-Rene Bernaudeau agreed: "You have to respect the yellow jersey. We will defend it as long as we can."

While Armstrong was unconcerned about the deficit he could not have expected to see four of his team mates crash in a major pile-up halfway through the stage.

ARMSTRONG ESCAPES

The crash, that occurred near the front of the main pack, also involved Italian sprint ace Alessandro Petacchi and second-stage winner Robbie McEwen but Armstrong escaped unscathed.

"A Liberty Seguros rider fell and sent four of our riders on the tarmac," said Bruyneel. "Happily, it's nothing serious."

The pile-up happened at the very moment the pack was launching an attack on the five-man breakaway -- Piil, O'Grady, Voeckler, Casar and Sweden's Magnus Backstedt.

Afterwards, the bunch, led by Armstrong's US Postal team mates, was far more cautious in the violent side winds and rain.

Of the first five home, Backstedt won the Paris-Roubaix classic this season, Voeckler took the French championship, Piil won a Tour stage last year in Marseille, O'Grady is one of the world's top sprinters while Casar is one of France's main cycling hopes.

On the finish line, O'Grady's finishing speed made the difference, allowing him to win his second Tour stage, six years after the first in Grenoble in 1998.

"This is a great victory, especially for my Cofidis team after the hard times we've been going through," the Australian said.

Cofidis have been rocked by a doping scandal in which their leader, Briton David Millar, has been caught up and banned from the race. He is also out of the Olympics after admitting taking a banned drug.

Voeckler will wear the yellow jersey in Friday's 196-km sixth stage between Bonneval and Angers, an honour he had never expected.

"I would lie if I said it was my ambition to take the yellow jersey," said Voeckler. "It's a strange feeling to wear it on top of the tricolour I've worn since the French championship.

"I will wear it for a day at least and hopefully more."