Voeckler, meanwhile, saw his lead in the yellow jersey cut ahead of today's return to France, losing crucial seconds after a wayward descent which saw him at one point lose control and go off into a roadside driveway.

Perhaps with his ego bruised by his off-road excursion, Voeckler said: "I lost time when I shouldn't have.

"Three times I went wide on a corner and the third time I was very, very lucky because I had to jump down a step that was about a metre high.

"I lost time and if I'd been more calm, I could have finished with the favourites but I was a little bit too ambitious."

The race favourites reduced Voeckler's lead by 27 seconds, with Cadel Evans (BMC Racing) at the front of the queue one minute and 18 seconds behind.

Voeckler expects to be relieved of the maillot jaune he assumed on stage nine when the overall contenders battle to today's summit finish at Galibier Serre-Chevalier.

The 200.5km 18th stage from Pinerolo includes the highest finish in the race's history at an altitude of 2,645 metres.

Voeckler added: "My climbing has been good but I don't think it's good enough. A 6km climb is a lot different to a 35km one."

Unlike Voeckler, Boasson Hagen had done his homework on Team Sky's reconnaissance in mid-June and mastered the precarious final run-in to Pinerolo to add the win to his stage six success.

The 24-year-old from Lillehammer was unfazed by a final 8km from the summit of the Cote de Pramartino labelled "fatally dangerous" by two-time Tour runner-up Andy Schleck before the stage.

Boasson Hagen, who indulges more in cross-country skiing than downhill during the winter, said: "I wasn't afraid of the descent because I've done it in training and watched it on video.

"I knew almost every corner and I was just looking forward to the finish.

"It was a really great feeling."

Meanwhile, Mark Cavendish (HTC-Highroad) extended his lead in the points classification by one and is 35 points clear of Jose Joaquin Rojas (Movistar) with four days of racing remaining.