Omega Pharma-Quick Step youngster Trentin proved the strongest of an 18-man breakaway, coming from behind to out-sprint Switzerland’s Michael Albasini (Orica-GreenEdge) and American Andrew Talansky (Garmin-Sharp).
Usually spotted leading out British team-mate Mark Cavendish in the big bunch sprints, 23-year-old Trentin was left to his own devices during the hilly 191km stage to become the third Omega Pharma-Quick Step rider to win on the 100th edition of the race after Cavendish’s double and Tony Martin’s victory in the individual time trial at Mont-Saint-Michel.
In his debut Tour de France, Trentin became the first Italian to win on the Tour since veteran sprinter Alessandro Petacchi won stage four of the 2010 race in Reims.
Yellow jersey Chris Froome (Team Sky) finished safely in the peloton seven minutes and 17 seconds in arrears to retain his race lead ahead of Sunday’s Bastille Day showdown on Mont Ventoux.
Julien Simon (Sojasun) – one of four Frenchmen in the leading group – looked on course for the victory after an audacious solo attack off the back of the final climb of the day, 10km from the finish.
But Simon was swept up just underneath the kilometre-to-go banner after a big effort from Marcus Burghardt of BMC. Albasini and Spaniard Jose Joaquin Rojas (Movistar) looked most likely to fight for the win, but Trentin’s late surge took them by surprise.
“I’ve always had a good sprint and working with Mark [Cavendish] has seen me pick up a thing or two,” said Trentin, whose Belgian team rode hard on Friday’s stage 13 to set up Cavendish for a second win amid the crosswinds of central France.
“Yesterday we worked so hard for Mark and so today I tried to conserve my energy on the climbs,” said Trentin. “But it wasn’t easy towards the end with Simon’s attack. I thought we had missed our chance.”
“It’s the fourth stage win for my team and the first for an Italian this year and for three years so I’m really happy,” he added.
The group of 18 escapees also included stage two winner Jan Bakelants, his RadioShack-Leopard team-mate Jens Voigt, French national champion Arthur Vichot and young Americans Talansky and Tejay van Garderen (BMC). It formed when an initial four-man break instigated by German veteran Voigt was joined by 14 chasers around 145km from the finish, ahead of the first of seven categorised climbs.
Combining well over the undulating roads of the Loire and Rhone, the leaders nevertheless struggled to open up a significant gap with Euskaltel, Lampre-Merida and Vacansoleil-DCM – who all missed the break – riding hard to reduce the gap.
With 100km remaining – and the gap just one minute for the leaders – Team Sky came to the front and urged the peloton to sit up. As a result, the escapees were given their ticket to ride off into the sunset.
Clearly angered by the decision, Dutch national champion Johnny Hoogerland (Vacansoleil), Italian veteran Damiano Cunego (Lampre) and Spain’s Juanjo Oroz (Euskaltel) attacked on the third climb of the day, 80km from the finish.
Oroz did not last long, but Hoogerland and Cunego managed to reduce the gap until the Dutchman rode clear of his fellow escapee on the next climb in solo pursuit of the leaders. Hoogerland managed to get within one minute of the front of the race before throwing in the towel and rejoining Cunego, with the break by now five minutes ahead of the main pack.
Both riders rode along in no-man’s land before being swept up by the peloton on the penultimate climb of the day, 15km from the finish.
Voigt, the oldest man in the peloton at 41, was the first of the 18 escapees to crack, followed shortly by Britain’s David Millar (Garmin-Sharp).
Van Garderen , Blel Kadri (Ag2R-La Mondiale) and Albasini were all chomping at the bit on the penultimate climb, but it was Simon who caught the leaders napping with an unexpected attack just after the summit of the urban climb on the outskirts of Lyon.
With Kadri in pursuit, Simon built up a lead of 28 seconds before Bakelandts, Lars Bak (Lotto Belisol) and Burghardt combined to reel him in on the long 2.5km home straight.
But having taken a back-seat in the break, Trentin was able to use his comparatively fresh legs to take a memorable victory in his first Tour de France.
The focus shifts to the battle for the yellow jersey on Sunday with the longest stage of the race, a 242.5km slog to Provence which culminates on the fearsome Mont Ventoux.
Froome leads Dutchman Bauke Mollema (Belkin) by 2:28 on GC, with Spanish rival Alberto Contador (Saxo-Tinkoff) in third place a further 17 seconds back.
The Team Sky leader was happy about the way his team controlled the peloton on a relatively straightforward day on Saturday.
“It was a hard start to the stage before the break formed but once they went ahead my team took charge of the peloton and it was fine,” he said.
Sunday’s queen stage will be an entirely different prospect: the legendary Ventoux is the longest climb of the Tour and comes at the end of the race’s longest stage – and on it’s open slopes there really is nowhere to hide.