AX 3 DOMAINES, France — At his first real opportunity, Chris Froome blew away his main Tour de France rivals with a supersonic burst Saturday, a fierce uphill climb that felt a little like the bad old days of Lance Armstrong.

But the Briton who took the race leader’s yellow jersey, and looks more likely than ever to keep it all the way to the finish in Paris on July 21, insisted there are fundamental differences.

Armstrong was stripped of seven Tour titles last year for serial doping. Froome promised that his achievements won’t need to be erased in the future.

“It is a bit of a personal mission to show that the sport has changed,” Froome said. “I certainly know that the results I’m getting, they’re not going to be stripped — 10, 20 years down the line. Rest assured, that’s not going to happen.”

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Froome hasn’t come out of nowhere. The 28-year-old was the Tour runner-up last year to teammate Bradley Wiggins, runner-up at the Tour of Spain in 2011 and has been the dominant rider this year coming into the Tour.

Drug testing in cycling is also better and more credible than it was when Armstrong and his U.S. Postal Service teammates were pumping themselves with hormones, blood transfusions and other banned performance-enhancers.

Froome leads Alberto Contador by nearly two minutes, with former champions Andy Schleck and Cadel Evans much further back, ahead of another tough mountain stage on Sunday.

In the overall standings, Froome is 51 seconds ahead of teammate Richie Porte and leads third-place Alejandro Valverde by 1:25.