The 36-year-old climber was followed up the 1,520-metre climb by team-mate Juan Jose Cobo, to register a third stage victory for the Italian team, after Riccardo Ricco’s victories at Super-Besse and Bagneres-de-Bigorre.
The Swiss-born Italian becomes the fourth man to win at the Pyrenean ski resort, after Luc Leblanc in 1994, Bjarne Riis in 1996 and Javier Otxoa in 2000.
CSC’s Frank Schleck came in third, 28 seconds behind Piepoli and Cobo, but Cadel Evans’ courageous ride ensures that he will wear the yellow jersey when the peloton departs from Lannemezan today.
Evans, of Silence-Lotto, showed few after-effects from his crash on Sunday, finishing one minute and 49 seconds behind Schleck, giving him an advantage of just one second over the Luxembourg rider in the general classification.
The Australian will be buoyed by the knowledge that every time the Tour has visited Hautacam, whoever has finished in yellow has gone on to win the race.
Incumbent leader Kim Kirchen limited his losses on the Tourmalet, but he could not keep pace with Evans’ group as the Hautacam began to hit hard. The Team Columbia rider is now one minute 56 seconds behind the yellow jersey.
The French crowds flocked to the slopes of the Pyrenees on Bastille Day, and they witnessed a son of Marseille, Remy Di Gregorio, take the first significant prize of the day by crossing the Tourmalet alone, claiming the Souvenir Jacques Goddet.
Di Gregorio led until 11 kilometres from the summit of Hautacam, when he was swallowed up by a chasing pack including Schleck, Denis Menchov and Carlos Sastre.
Less fortunate were Alejandro Valverde and Damiano Cunego, whose hopes of reaching Paris in yellow were hit by a five-man assault by Team CSC on the Tourmalet.
Piepoli’s victory comes a day after Ricco’s, with ‘the Cobra’ correctly predicting that his fellow countryman would take the summit victory.
“It is true that Ricco had said I would win here, but in reality it’s just a coincidence,” Piepoli said.
“These things are never pre-determined, our directeur sportif is not a magician! I have already been fifth in a stage of the Tour, and I already have good memories of the event. But I still have dreams and to win a stage goes some way towards achieving one. Today this was better than a dream.”
Neither Mark Cavendish nor David Millar were suited to the harsh climbs, with both eager just to finish in order to challenge for stage wins when the Tour leaves the haute-montagnes.
Millar came in 132nd, 33 minutes and 14 seconds behind Piepoli, while Cavendish suffered a collision in the opening 10km and eventually came round in last place, 34 minutes 55 seconds back.
The 23-year-old from the Isle of Man said after his stage win in Toulouse that he was eager to stay in the race until Paris in order to chalk up an third stage win, which would be unprecedented for a single British rider in the same Tour.