ALPE d’HUEZ, France — After 2,105 miles and nearly three weeks of racing, through three perilously steep climbs into the Alps, the Tour de France will be decided Saturday in a 26-mile sprint through Grenoble. This is like deciding a marathon with a 100-meter dash.

The potentially dramatic situation emerged Friday when, in the final mountain stage of this year’s Tour, Andy Schleck of Luxembourg secured the overall leader’s yellow jersey, which has long eluded him this late into the competition. Unlike in the previous two Tours, he will not enter the penultimate and decisive stage behind Alberto Contador of Spain. But Cadel Evans of Australia lurks close behind, 57 seconds out, and he is considered a superior time trialist.

One by one, in reverse order of the standings, the riders will set out Saturday in an individual time trial, the ultimate race against the clock. Their teammates will not be around to pull them along, as they dutifully did through ascents in the Pyrenees and the Alps.

Whoever stands on top after Saturday will be sipping Champagne on Sunday during the final stage, a ceremonial ride into Paris.