One key rival down for Lance Armstrong, at least four others to go.

Armstrong turned two treacherous cobblestone stretches of the Tour de France to his advantage Tuesday, while Spain's Iban Mayo crashed in a blow to his title hopes.

But other challengers, including German Jan Ullrich, American Tyler Hamilton, Italy's Ivan Basso and Spain's Roberto Heras, could still derail Armstrong's attempt for a record sixth straight crown.

"Ugh, that's unbelievable," the Texan said in summing up the difficult day.

French sprinter Jean-Patrick Nazon won the third stage and Australian speedster Robbie McEwen took the overall race lead, 16 seconds in front of the fifth-place Armstrong.

But Mayo's disaster was the big news of the day, and resulted in him losing 3 minutes 48 seconds to Armstrong.

Mayo crashed in a dash by the main pack of riders to be first onto the dangerous bumps, and couldn't make up the lost time even though he resumed racing in torn shorts.

"It's terrible," said Julian Gorospe, manager of Mayo's Euskaltel-Euskadi team. "He fell at the worst time in the race, when everyone wanted to be near or at the front."

The 26-year-old Mayo is a fearless climber and could regain time in the Pyrenees and Alps later in the three-week race. Armstrong has said he favors Mayo to win a mountain time trial four days before the finish in Paris on July 25.

But four minutes? Armstrong and the other top challengers would have to experience disasters of their own for Mayo to stand atop the winner's podium. Mayo risks falling further behind Wednesday, in a team time trial where his squad is expected to struggle.

"Today, you could not win the Tour de France but you could lose the Tour," Armstrong's manager, Johan Bruyneel, said. "Almost four minutes for Mayo is a very, very important gap."

Armstrong's U.S. Postal Service team performed well in the 130-mile race from Waterloo, Belgium, to Wasquehal, and helped to shepherd their leader over the dangerous cobblestones.

The team was the first to negotiate the initial 1.7-mile bumpy path, and was near the front of the pack at the second section about 15 miles from the finish.

"It's just a matter of fighting. You have no friends except your teammates," said Postal veteran George Hincapie, his face caked with grime. "We wanted to get to the cobblestone section first, just like the rest of the 200 guys. . . . We did it. Lance was right on my wheel and it worked out great."

Armstrong was grateful for the teamwork.

"I had some experienced guys there to help me," Armstrong said.

Mayo was 151st out of the 184 riders who finished. He trails Armstrong by 4:07 after four days of racing. Armstrong will duel for the lead with Ullrich and the other remaining challengers in later mountain stages and time trials.

Ullrich and Armstrong finished with the same time Tuesday, five seconds behind Nazon. The French rider's stage win was the second of his Tour career. He also won the prestigious sprint on the Champs-Elysees in Paris at the finish last year.

Overall, Armstrong still carries a narrow 15-second lead over Ullrich, 16 seconds over Hamilton, 27 seconds over Basso and 35 seconds over Heras, the Texan's former teammate who now leads a squad of his own. Armstrong built those time gaps with a speedy second-place finish in the debut time trial that began the Tour last Saturday.

McEwen, winner of Monday's stage, took the overall race lead on Tuesday and the cherished yellow jersey that goes with it because of time bonuses earned from his sprinting. But his goal is to win the green sprinter's jersey at the finish in Paris. He is not a threat for the overall title.

"I would have preferred to have won the stage. But it's great to wear the yellow jersey in the Tour de France. It's a first for me," the 32-year-old Australian said. "It was a difficult stage. Very hard."

At least four other riders were caught in the crash that took down Mayo. They included Italian Marco Velo, whose Tour ended with him nursing a broken collarbone in a roadside ditch.

The cobblestones usually form part of the Paris-Roubaix race, a grueling classic known as "the Hell of the North." Not since 1985 had the Tour veered onto cobblestones. Some teams and riders complained that they should not have been included in cycling's showcase race.

Iban Mayo of Spain, sporting a gaping hole in his shorts and scrapes from a fall that cost him nearly 4 minutes, struggles to catch up with the pack.