Lance Armstrong's pursuit of a record sixth Tour de France victory gained momentum on Tuesday when he won the first Alpine stage to reclaim the yellow jersey from Thomas Voeckler.

The American beat his main rival Ivan Basso in a dramatic sprint finish at the end of the gruelling 180.5-km 15th stage between Valreas and Villard-de-Lans, to snatch the 18th stage win of his career in the world's most famous cycling event.

Jan Ullrich, the German 1997 Tour champion, was third, crossing the line three seconds behind Armstrong and Basso.

"I don't think it's over," the Texan said with a smile.

"Ivan is riding super. It's not over. I think Ivan can ride a good race tomorrow," he said.

With a decisive 15.5-km individual time trial at l'Alpe d'Huez to come on Wednesday, Basso appears to be the only man capable of stopping the U.S. Postal rider.

The Italian held off Armstrong to win the 12th stage in the Pyrenees resort of La Mongie and came a close second to the American the following day. He is now second overall, just one minute and 25 seconds behind Armstrong.

Spaniard Iban Mayo, who won the Alpe d'Huez stage last year and would have been expected to again do well there, withdrew from the Tour before Tuesday's stage, complaining of exhaustion.

TOO TOUGH

The seven climbs scattered on the day's route proved too tough for Frenchman Voeckler, who finally relinquished the yellow jersey after 11 days.

The 25-year-old, who had a slim 22-second lead at the start, finished nine-and-a-half minutes behind Armstrong and now lies eighth overall.

"I'm not too disappointed because I knew it was bound to happen. When the real fight started I knew it was over," Voeckler said.

Third overall is German Andreas Kloeden, who finished fourth on Tuesday after he was helped by team mate Ullrich.

Ullrich had managed to attack Armstrong on the first category Echarasson climb, briefly opening up a gap of 1:09 before Basso's team mates worked hand in hand with the U.S. Postal team to reel him in.

"With the help of my team mates Floyd Landis and Jose Azevedo and with Ivan's team mates, we never were in trouble," Armstrong said.

"We knew the course very well and for us it was not really a threatening situation," he said.

Kloeden also tried to launch an attack with 500 metres to go but Armstrong reacted in merciless style, surging past the German and Basso to show he was still the undisputed boss.

It was the 32-year-old's 61st yellow jersey.

"I still remember when I put on the first one and I was the happiest man in the world, that would have been enough for me to take to the grave," he told Eurosport television.

"Hopefully I'll have it for another five days."