Two attacks towards the business end of a rolling 187.5km stage through the Jura mountains saw Lotto Belisol's Gallopin hold off the peloton by a bike length to add a career first Tour stage victory to the yellow jersey he wore on Bastille Day on Monday.
Germany's John Degenkolb (Giant-Shimano) outsprinted Italians Matteo Trentin (Omega Pharma-Quick Step) and Daniele Bennati (Tinkoff-Saxo) to take second place in the ensuing bunch sprint.
Peter Sagan, the green jersey from Cannondale, missed out on yet another gilt-edged chance to open up his account after a dispute with Michal Kwiatkowski (Omega Pharma-Quick Step) and Mick Rogers (Tinkoff-Saxo) scuppered the chances of the chasing trio as they passed under the flamme rouge.
Gallopin made his initial attack on a wooded uncategorised climb 14km from the finish before starting the descent with a small gap over the streamlined peloton. Sagan, Kwiatkowski and Rogers led the chase, the trio drawing level with Gallopin on the outskirts of Oyonnax with 4km remaining.
But with 2.5km remaining, 26-year-old Gallopin surprised with a second attack - and it proved decisive. Sagan and Kwiatkowski - two riders with a frosty history - marked each other, while Rogers clearly knew he had no chance in a sprint.
As Gallopin dug deep entering the final straight, an exasperated Sagan gesticulated in frustration and sat up. The Slovakian tyro finished ninth place and cut a forlorn figure when later taking to the podium to accept his green jersey.
Gallopin thanked his family, girlfriend (Marion Rousse, the professional women's rider and Eurosport pundit) and team - plus paid tribute to the late Laurent Fignon - after his "unbelievable" win. The Frenchman also said that he had done a recon on the stage with his Lotto Belisol team-mates and so knew exactly where he wanted to attack.
"Today I thought I might have a chance but I never expected that. I'd never have imagined both a yellow jersey and a stage win coming onto this Tour," he added.
Italian race leader Vincenzo Nibali (Astana) finished safely to retain his yellow jersey as world champion Rui Costa (Lampre-Medira) dropped out of the top ten after being distanced on the fast final descent.
THREE-MAN BREAK: Under blue skies and hot sun, a fast and furious start to the stage saw IAM Cycling try to force early breaks through Jerome Pineau and Sylvain Chanavel. Peter Sagan, the green jersey, also had a solo dig before the day's main break formed. Unsurprisingly, IAM Cycling were present - this time through Swiss national champion Martin Elmiger, who edged clear after about 25km with French duo Cyril Lemoine (Cofidis) and Anthony Delaplace (Bretagne-Seche).
The trio built up a maximum lead of 6:45 before Elmiger rode clear on the first of four categorised climbs, the Col de Rogna, 48km from the finish. Tom-Jelte Slagter (Garmin), Jesus Herrada (Movistar), Jan Bakelants (Omega Pharma-Quick Step), Cyril Gautier (Europcar) and Nicolas Roche (Tinkoff-Saxo) attacked from the peloton, which had cut the deficit to less than a minute.
Stagter dropped back but the other four chasers joined Elmiger on the front of the race on the penultimate climb, 38km from the finish. Roche was the last man caught by the peloton - the Irishman swallowed up after Germany's Tony Martin (Omega Pharma-Quick Step) upped the pace on the descent of the Cote d'Echallon.
Gallopin was primed, however, to launch his own move as the road ramped up one final time ahead of the final 12km downhill ride to the finish.
RIDE OF THE DAY: It seems churlish to deny Tony Gallopin this award after the Frenchman's brilliant victory - but special mention must go to American Andrew Talansky, who was dropped by the peloton with 85km remaining. His body battered and bruised by two large falls, Talansky toiled in the hear, at one point getting off his bike and sitting on the guardrail of the road as if destined to throw in the towel. But last month's Criterium du Dauphine winner remounted in tears and bravely rode the rest of the stage in solitude, eventually coming home more than 32 minutes down on Gallopin.
DAY TO FORGET: Once again, Peter Sagan was caught out on the finish - the race's most consistent rider missing out on another opportunity to take the victory. Afterwards, Sagan admitted that it's getting "harder ever day because everyone knows me and my strengths. Kwiatkowski, Rogers and Gallopin are strong riders and none of them wanted to work because I would have won the sprint. But if we slowed for a bunch sprint then it would have been hard for me."
COMING UP: Friday's 185.5km rolling stage 12 from Bourg-en-Bresse to Saint-Etienne is another leg-sapping test that features four lower category climbs ahead of a fast and flat finish.
PLAT DU JOUR: Bresse is renowned for its poultry and so a nice Coq au Vin will do the trick, followed by an apple and blueberry tart from Pilat near Saint-Etienne.
- Sports & Recreation
- Omega Pharma-Quick Step
- Peter Sagan
- Michal Kwiatkowski
- Lotto Belisol
- Mick Rogers