Race leader Tony Martin broke his collar bone in a crash that puts his involvement in the Tour de France in jeopardy after Czech Zdenek Stybar of the Etixx-Quick Step won the sixth stage.
Slovakian Peter Sagan of Tinkoff-Saxo was second and Frenchman Bryan Coquard of Europcar finished third in a crash-marred finale.
Martin required the support of three team-mates to remount his bike and cross the line in the yellow jersey, while cradling his left arm after landing on his shoulder.
Replays suggested Martin caused the crash 900m out which also saw defending champion Vincenzo Nibali (Astana) tumble to the Tarmac, with the peloton fracturing behind.
He later confirmed that he had broken his collar bone, and his race could now be at an end on another bittersweet day for Etixx-QuickStep.
"Collarbone is broken. We will discuss further steps," Martin wrote on Twitter.
If Martin's race is over - as appears likely - he will be the second leader to abandon this year's race while in the maillot jaune, after Fabian Cancellara's crash on stage three.
Mark Cavendish, the Belgian squad's leader, was beaten on Wednesday in a sprint finish he had been expected to win.
Cavendish could have another chance in tomorrow's 190.5km stage from Livarot to Fougeres as he chases a 26th Tour stage success and first in nearly two years.
The possible absence of Martin would be a big blow for the Manxman, though.
If Martin is forced to withdraw, Team Sky's Chris Froome would inherit the race lead.
Froome remained 12 seconds behind Martin as the top of the general classification remained unchanged - with the crash inside the final three kilometres of the stage seeing all riders awarded the same time.
The day's three-man break included Eritrean Daniel Teklehaimanot (MTN Qhubeka), France's Perrig Quemeneur (Europcar) and Kenneth van Bilsen (Cofidis) of Belgium.
Thomas Voeckler (Europcar) attempted to counter attack after the intermediate sprint, but soon was back in the peloton.
Teklehaimanot then claimed the point at the third and final categorised climb of the day to assume the polka dot King of the Mountains jersey from Joaquim Rodriguez, who won at the Mur de Huy on Monday.
Van Bilsen attempted to accelerate away in the closing 12km as his escape companions were swallowed up by the charging peloton.
His slender advantage was being chipped away and stood at 10 seconds with 4km to go and he was caught a kilometre later.
The battle for positioning began in earnest, with John Degenkolb's Giant-Alpecin squad on the front and Martin, in the maillot jaune, behind him.
Martin's Etixx-QuickStep squad took over, with Cavendish on third wheel, but the Briton was overtaken as the sharp climb to the finish began 1.3km out.
Martin was on the left side of the road when he veered right and careered into another rider who in turn toppled Nibali. Others followed.
Stybar managed to sneak through and stole a march to win by two seconds from Peter Sagan (Tinkoff-Saxo), who was second for a second successive day.
Bryan Coquard (Europcar) was third and Degenkolb fourth.
Dan Martin finished the stage in 47th, two seconds behind the winner. Nicolas Roche and Sam Bennett were 165th and 166th, respectively, both finished three minutes and 20 second behind Stybar.
Stage 6 (Abbeville - Le Havre, 191.5 km): 1. Zdenek Stybar (Czech Republic / Etixx - Quick-Step) 4:53:46" 2. Peter Sagan (Slovakia / Tinkoff - Saxo) +2" , 3. Bryan Coquard (France / Europcar) 4. John Degenkolb (Germany / Giant), 5. Greg Van Avermaet (Belgium / BMC Racing) , 6. Tony Gallopin (Franc /Lotto), 7. Edvald Boasson Hagen (Norway / Team MTN), 8. Davide Cimolai (Italy / Lampre), 9. Julien Simon (France / Cofidis), 10. Gorka Izagirre (Spain / Movistar).
General Classification: 1. Tony Martin (Germany / Etixx - Quick-Step) 22:13:14", 2. Chris Froome (Britain/Team Sky) +12", 3. Tejay van Garderen (US /BMC Racing) +25" , 4. Peter Sagan (Slovaki /Tinkoff - Saxo) +27", 5. Tony Gallopin (France / Lotto) +38", 6. Greg Van Avermaet (Belgiu /BMC Racing) +40", 7. Rigoberto Uran (Colombia/Etixx - Quick-Step) +46" , 8. Alberto Contador (Spain/Tinkoff - Saxo) +48", 9. Zdenek Stybar (Czech Republic/Etixx - Quick-Step) +1:06", 10. Geraint Thomas (Britain/Team Sky).
