Slovakian prodigy Peter Sagan claimed a shortened third stage of the Paris-Nice race on Wednesday while Alberto Contador showed in a nervy finale he had regained confidence two days after crashing.

The twice Tour de France champion lost balance in the final sprint after 153 km from St Yrieix La Perche but somehow managed to stay on his bike to cross the line in sixth place after catching his main rivals off guard.

The 20-year-old Sagan, who showed his class earlier this year at the Tour Down Under, was too strong in the last stretch for Spaniard Joaquim Rodriguez and Ireland's Nicolas Roche, who finished second and third respectively.

"I am very happy to get my first victory in the ProTour. After the Tour Down Under, I thought I would not be in great shape but obviously it went well", Sagan, who is second overall, told reporters.

"There are still four tough stages remaining so let's not get carried away."

Contador was in a group of six that broke clear from the pack in the final ascent of the day and is now sixth overall, 20 seconds behind German Jens Voigt, who snatched the yellow jersey from Dutchman Lars Boom.

"I am happy with this stage," said Contador, who bruised his leg in a crash on Monday.

"The goal was not to test myself today but an attack was launched in the last ascent and the bunch could not follow the pace so I took my chance."

Snowfalls in the Limousin region forced organisers to shorten the stage from 208 to 153 km, a common move on the 'Race to the Sun'.

Frenchman Yann Huguet broke clear after 33 kilometres and was quickly joined by Belgians Jurgen Roelandts and Nikolas Maes as the trio bult a seven-minute gap on narrow and winding roads.

The Caisse d'Epargne team, with Alejandro Valverde and last year's winner Luis Leon Sanchez bidding for overall victory, led the chase.

Maes was the first to surrender, with Roelandts and Huguet being caught with six kilometres left.

Roche attacked in the Cote de la Maritinie less than four kilometres from the finish and was joined by a group of four, including Contador.

The Astana rider regained four seconds from Sanchez, who failed to sustain the pace in the climb, on the eve of the toughest stage, a 173.5-km trek to Mende with a mountain top finish.

He did not even try to sprint for the stage victory that went to Sagan, the youngest rider in the race.

Contador said he was touched by German Tony Martin so he lost his balance.

"He touched me and I did my best to stay on the bike. That's the only disappointing side of the day," said the Spaniard, who finished the stage two seconds behind Sagan.