Luz-Ardiden, France ? His yellow jersey smeared with dirt after a fall, Lance Armstrong got back on his bike with a fierce look that said it all: The Tour de France is slipping away. It’s now or never.

Riding like the four-time champion he is, Armstrong overcame a hard crash and two weeks of lackluster form to tear away from his closest challengers Monday and set cycling’s premier race up for a gripping finale.

In its 100-year history, the Tour has witnessed many epic days, but few like this.

A spectator knocked Armstrong off his bike just as he was accelerating away from archrival Jan Ullrich in the day’s last ascent, to the ski resort of Luz-Ardiden high in the misty Pyrenees.

His left elbow grazed, the 31-year-old Texan picked himself up, remounted and, fueled by the adrenaline of the crash, stormed past Ullrich to perhaps save his chances of equaling Miguel Indurain’s record of five successive Tour wins.

Armstrong had gone into the stage, the 15th of 20 in the three-week Tour, with his overall lead hanging by a thread. Ullrich, the 1997 winner, was just 15 seconds back and gaining momentum, while Armstrong had struggled for days.

When he crashed, Armstrong said he told himself: “‘Lance, if you’d like to win the Tour de France, it’s today.'”

He crossed the line 40 seconds ahead of Ullrich, slumped over his handlebars, drained. Overall, thanks to bonus time he got for finishing first, Armstrong widened the gap over the 29-year-old German to 67 seconds — giving him a vital cushion for crucial days ahead to the finish Sunday in Paris.

But he could do without the drama. This has been a hard Tour for Armstrong. He battled stomach flu before the start July 5; he was bruised in a crash the second day; he failed to shine in the mountains where he usually dominates; he was crushed by Ullrich in a time trial last Friday.

“This has been a Tour of too many problems, too many close calls, too many near misses, too many things that seem like they’re worth a lifetime,” Armstrong said. “I just wish it would stop. I wish I could have some uneventful days. But anyway it was a good day today.”

American Lance Armstrong strains during the final ascent of the 15th stage of the Tour de France. Armstrong won the stage and increased his overall lead during Monday's race between Bagneres-de-Bigorre and Luz-Ardiden, France.

The stage win was Armstrong’s first of this Tour, apart from an earlier team time trial victory, and put his career total at 16.

His dominant ride effectively knocked his second-closest rival, Alexandre Vinokourov of Kazakhstan, out of the running, and gave Armstrong a much-needed cushion going into the last time trial Saturday.

Ullrich, an excellent time trialer, bit a whopping 96 seconds out of Armstrong’s overall lead in that event last Friday. Armstrong feared if his lead over Ullrich stayed at 15 seconds before Saturday’s race against the clock, his Tour could be lost. That left the Texan, an excellent climber, little choice but to attack on the lung-burning 8.3-mile ascent to Luz-Ardiden in hopes of widening the gap.

“I was a little bit desperate because I knew I needed to make the race today in order to put some more time into Jan,” Armstrong said. “I knew today was a very big day for me. … and that if I wanted to win the Tour de France, it was necessary to go all out and attack.”

But about 5.9 miles from the finish, a spectator’s outstretched bag caught Armstrong’s handlebars, toppling him. Armstrong hit the tarmac heavily, but was not badly hurt. He said the fall was partly his fault because he was shaving the huge, excited crowd that lined the winding ascent. Iban Mayo of Spain crashed into Armstrong as he lay in the road and fell, too.

The drama didn’t stop there. Shortly after climbing back on his bike, Armstrong’s right foot slipped out of his pedal and he nearly fell again.

Overall leader Lance Armstrong celebrates on the podium after winning the 15th stage of the Tour de France. Armstrong held off two rivals in a riveting climb Monday in the Tour de France between Bagneres-de-Bigorre and Luz-Ardiden, French Pyrenees.

Ullrich, who had to swerve to avoid Mayo and Armstrong’s crash, proved to be a gentleman, waiting with other riders while Armstrong and Mayo caught up. Armstrong thanked his rival but recalled that he had also slowed down for Ullrich when he crashed on a steep descent from a mountain pass in 2001.

“Jan is a good guy, he’s an honorable guy,” Armstrong said. “As we say in English: ‘What goes around comes around,’ and so I appreciate him doing that.”

Ullrich, however, may regret his sportsmanship.

Armstrong threw himself onto his pedals after recovering, powering past Ullrich and other riders up the mountain into the mist, his eyes fixed determinedly on the road ahead. His legs whirring, a silver cross bouncing on his chest, Armstrong widened the gap as he ascended: 15 seconds, 20, 40. This was classic Armstrong, reminiscent of some of his great climbs of past Tours.

“Lance is back,” said Floyd Landis, his U.S. Postal teammate.

The ferocity of Armstrong’s attack caught Ullrich by surprise, said his teammate, Aitor Garmendia. He also said Ullrich “was certainly thrown off by Lance’s fall. It broke his rhythm.”

But “the race is still open. Ullrich has had an incredible last few days and he’s a bit tired today,” Garmendia said. “He’ll recover. Never has he been so close to Lance.”

Ullrich finished the stage third, behind Mayo, who also recovered from the crash. But Vinokourov was eighth, his mouth gaping open in exhaustion, dropping 2 minutes, 45 seconds behind Armstrong overall. He had been just 18 seconds back at the start of the day.

Today is a rest day before a final day Wednesday in the Pyrenees. The other stages to Paris are mostly flat and do not offer riders easy chances to make up much time. The only exception is Saturday’s time trial, which will likely decide — barring more unforeseen dramas — whether Armstrong or Ullrich wins.