Young Slovak sensation Peter Sagan avoided the cross-the-road pile-up to claim his third stage win in a sprint finish. Fabian Cancellara of Switzerland also rode clear of the mess to retain the yellow jersey.
The 129-mile ride from Epernay to Metz got off in the Champagne region of France as roadside fans held aloft glasses of bubbly to cheer on the riders.
But as the pack picked up speed to chase four breakaway riders with about 16 miles to go, at least two dozen riders spilled across a rural road -- leaving many downed, dazed or looking for team staffers for support in a jumble of injured riders and bikes on the ground.
"It was like a trench hit by a (grenade) when I entered the crash to give my bike to Bauke," said Rabobank's Laurens Ten Dam on his Twitter account of the crash and his teammate Bauke Mollema. "Lots of blood and screaming. Carnage."
The Garmin squad, riding in formation, bore the brunt.
Tom Danielson, who finished in last year's Tour in eighth place, was already nursing a separated shoulder from a crash earlier in the week. In Friday's spill, he was briefly knocked unconscious, and later rushed to a hospital for hip, collarbone and elbow injuries. He was one of at least four riders to drop out of the race because of the crash.
"It was the scariest crash I've ever been in," Garmin veteran David Millar said. He had black marks of chain-grease all over his arm and said the riders were going at least (43 miles) an hour when the crash occurred.
"God knows how it happened," Millar said.
Meanwhile, Garmin's Ryder Hesjedal of Canada -- the winner of the Giro d'Italia in May -- injured his knee and lost more than 13 minutes in the hunt for the title, all but quashing his podium ambitions. He had started the stage in ninth place, 18 seconds back.
Two other contenders, Bradley Wiggins and defending champion Cadel Evans, escaped unscathed.
Overall, Cancellara leads ahead of Wiggins -- a pre-race favorite, hoping to become the first Briton ever to win the Tour -- by seven seconds. Evans climbed one spot to sixth, and is now 17 seconds back, after Edvald Boassen Hagen of Norway lost more than two minutes in a crash.
The peloton, led by sprint teams from Orica-GreenEdge and Lotto-Belisol, then caught four breakaway riders with just over a mile to go. Andre Greipel of Germany, who is hoping for a third consecutive stage win, was the first to make a move in the final section, but couldn't resist Sagan's surge.
"I was in a good position, I kept it and then nothing hampered my effort," Sagan said. "I took Greipel's wheel and everything went according to plan."
Garmin had one bright spot: U.S. rider David Zabriskie launched an attack 3 miles after the start, and was joined by three other riders.
The four breakaway riders collaborated well and built a four-minute lead over the peloton before Cancellara's teammates moved to the front of the bunch to set up a faster tempo.
But the day's first crash 22 miles into the stage that involved at least 20 riders upset the chase, and the escapees' advantage grew to more than six minutes after 26 miles.
Among those caught in that crash were Rabobank team leader Robert Gesink, winner of the Tour of California this year, and former Spanish Vuelta champion Alejandro Valverde of Spain. But all the riders involved in the pileup to have gotten back on their bikes.
Another minor crash slowed the peloton with 37 miles to go, with Greipel hitting the ground.
Zabriskie, who earned honors as the stage's most competitive rider -- held out alone leading the breakaway until sprinters from the depleted front pack overtook him.
The race moves into the mountains on Saturday with a 123-mile ride to the ski resort of La Planche des Belles Filles in the Vosges. The stage features the Tour's first category-one climb, a tough 4-mile ascent with the final few hundred yards at an average gradient of 14 percent.
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