After a series of second-places in the opening week of the race, Sagan finally got a win after a textbook day for his Cannondale team.
Sagan, 23, picked up maximum points at both the intermediate sprint and the finish after his big rivals Mark Cavendish (Omega Pharma-Quick Step), Andre Greipel (Lotto-Belisol) and Marcel Kittel (Argos Shimano) were all distanced on the second of four categorised climbs, 90km into the undulating 205.5km stage from Montpellier to Albi.
At the finish, Sagan latched onto Degenkolb's wheel before powering clear inside the final 100m to cross the line all smiles while beating his chest in celebration.
Daniele Bennati (Saxo-Tinkoff) took third place ahead of fellow Italian Davide Cimolai (Lampre-Merida) and Norway's Edvald Boasson Hagen (Team Sky).
South Africa's Daryl Impey of Orica-GreenEdge retained the yellow jersey after finishing safely in the main peloton.
Victory for Sagan saw him extend his lead in the green jersey competition to 94 points over German national champion Greipel, with British champion Cavendish another 11 points in arrears.
Both Cavendish and Greipel came home in a grupetto more than 14 minutes down on the peloton after giving up the chase 45km from the finish, when the gap was still three minutes and showing no signs of coming down.
A relieved Sagan was quick to praise his Cannondale colleagues for their role in his first win of the stage: "I'm very happy and I have to thank my team because I couldn't do what I did without them. This victory is for all of the team. I'm very happy because I didn't feel very good after the crash on the first stage but day by day I'm feeling better and now I'm really happy to have my first stage win of this Tour de France."
On another hot day in south France, two riders broke clear shortly after the start, with the race’s oldest rider Jens Voigt (RadioShack-Leopard) joining forces with Blel Kadri (Ag2R-La Mondiale) to carve out a large lead over a peloton disrupted by a large pile-up as the road narrowed over a bridge.
American Christian Vande Velde, riding his last Tour before retiring, was once again caught up in the melee and the 37-year-old Garmin-Sharp rider was forced to bid an early farewell to the Grande Boucle after an accumulation of injuries sustained during an incident-filled opening week.
Riding his 16th consecutive Tour, 41-year-old German Voigt and France’s Kadri held a four-minute gap over the peloton after the first climb of the day, 128km from the finish. Kadri picked up maximum points over the summit, and repeated the feat on the subsequent Cat.2 climb to move into the lead in the polka dot jersey competition.
But behind the two escapees, the race was being blown apart by the Cannondale team of Sagan, who threw down the hammer on the Col de la Croix de Mounis to wreak havoc off the pack of the peloton.
The infernal pace of Cannondale saw Sagan’s sprint rivals Cavendish and Greipel – the winners of the previous two stages – as well as stage one winner Kittel and Australian Matt Goss (Orica-GreenEdge) all distanced on the long climb.
A Greipel-chasing group came over the summit almost two minutes down on the main pack, while a second Cavendish group came through another minute in arrears. The distanced factions came together on the back of the climb, with Lotto Belisol and OPQS joining forces in the chase ahead of the intermediate sprint.
Sagan picked up a maximum 20 points at the intermediate sprint 70km from the finish ahead of Vacansoleil-DCM’s Juan Antonio Flecha. With Cannondale taking a little breather, Belgium’s Jan Bakelants (RadioShack-Leopard) accelerated clear.
The stage two winner and former race leader was joined by France’s Cyril Gautier (Europcar) and Spaniard Juanjo Oroz (Euskaltel) in a trio that soon held a one-minute lead over the pack, putting Bakelents into the virtual race lead.
With Orica-GreenEdge coming to the front to help neutralise the threat to Impey’s yellow jersey, the gap back to the chasing group of Cavendish and Greipel increased to three minutes.
Perhaps thinking about the mountains on the horizon, Lotto Belisol and OPQS decided to call off the chase ahead of the final climb of the day. Bakelants led the trio over with a 45s cushion, but the Cannondale-led peloton timed their chase to perfection, sweeping up the leaders with 3km remaining before setting things up for their man Sagan.
With two Argos team-mates at his disposal, Degenkolb at least made the finish a contest – but Sagan had too much strength and, after three second-places on the100th edition of the Tour, the Slovakian was not going to let this chance slip.
Sagan’s victory was the cherry on the cake for Cannondale, who put in a display of tactical brilliance not only to kill off their main rivals but to deliver their man to the line in style. With the exception of one slight wobble on a roundabout on the outskirts of Albi, it was a flawless performance – and better than any collective effort seen so far in the 2013 Tour.
Focus turns from the sprinters to the climbers and GC hopes on Saturday, with the first major summit finish of the race. The 195km stage from Castres to the Pyrenean ski resort of Ax 3 Domaines includes the highest point in the race, the HC Col de Pailheres.
With Sky’s Chris Froome and Saxo-Tinkoff’s Alberto Contador just eight and 14 seconds down on GC respectively, we can expect one of the big race favourites to don the yellow jersey.