(CNN) -

Mark Cavendish sprinted to a superb victory in Stage 18 of the Tour de France. With a few hundred meters remaining the Team Sky rider broke clear of the peloton and chased down the front runners to claim an impressive second win of this year's Tour.

Cavendish, a sprint specialist who will represent Brtain at the forthcoming Olympic Games, has spent a lot of the Tour supporting team mate Bradley Wiggins' attempt to claim the overall title, but in Friday's stage he benefited from his colleagues' strategy.

"I've had a lot of desperation for a sprint as we haven't had a lot for me to do this year," he told the Tour website.

"It was always going to be close at the end because there were a few guys still away but the team rode perfectly and Brad timed it so we'd catch them in the last kilometer."

Cavendish's victory in the 222.5 km stage between Blagnac and Brive-la-Gaillarde was his 22nd stage win at the Tour, moving him fourth in the all-time records. He is now level with American Lance Armstrong and legendary French sprinter Andre Darrigade.

"Twenty-two stage wins... has it sunk in? Yeah! Because I've been waiting to do it for nearly three weeks now," Cavendish told the Tour website.

"I'm now equal with André Darrigade: he won 15 sprints but 22 stages of the Tour de France. So to match him is something, it makes me happy"

Overall leader Bradley Wiggins finished just behind his colleague to ensure his two minute five second lead remained intact. With two stages remaining, it would be a major surprise if Wiggins didn't become the first Britain to win the tour when it reaches its conclusion on Sunday, in Paris.

The first incident of the day occurred 120 km into the stage when a large dog ran onto the course, causing a crash.

Four riders were unseated in the incident, notably Philippe Gilbert of the BMC team.

The former Belgian national champion took a moment to remonstrate with the dog's owner before climbing back onto his bike. Gilbert later received treatment during the race from Tour medical staff.

Team RadioShack-Nissan rider Franck Schleck, who withdrew from this year's Tour after a failing a doping test, has protested his innocence after announcing that his 'B' sample also tested positive.

"The result of the counter test was positive, but for me nothing changes," he said in a statement.

"I just know that I did nothing wrong. I will therefore continue my search to find out ho the substance could have entered my body."

Luxembourger Schleck, whose brother Andy won the 2010 tour when Alberto Contador failed a doping test, was 12th when he retired from the race.