With a stunning final dash of speed, Armstrong snatched victory from German Andreas Kloden at the end of the Tour's hardest Alpine stage, pedaling so furiously that his bicycle swung wildly beneath him.
The win Thursday was Armstrong's fourth this Tour -- matching his best in previous years which he also dominated -- and his third in three consecutive days where the cancer survivor has all but locked up a record sixth-straight crown.
It also was perhaps the most incredible. Even Armstrong seemed to find his sprint finish hard to believe. A beaming smile on his face, he jubilantly pumped his fists in the air as he zoomed past Kloden, who seemed destined to win until Armstrong edged him at the line.
"No gifts this year," said the five-time champion. "I want to win."
Aside from satisfaction, the victory earned Armstrong 20 bonus seconds that helped extend his already sizable overall lead on Italian Ivan Basso to 4 minutes, 9 seconds.
Barring disaster, that is more than enough to carry the Texan through to the finish in Paris on Sunday to become the only six-time winner of the 101-year-old cycling marathon.
"Sweet," he told teammate Floyd Landis as they hugged at the finish.
"You're the man. Nice sprint. I'm glad you got it," Landis replied.
Armstrong's original plan had been to let Landis win. But in the end, the chance for a 20th career individual victory in his favorite cycling race was too good to pass up.
At the top of the last of five climbs on Thursday's 204.5-kilometer (126.8-mile) trek through the Alps, Armstrong reached an arm over to Landis and told him to try for what would have been his first Tour victory. The finish was 13 kilometers (8 miles) away, at the end of a long, speedy descent to Le Grand-Bornand.
"I said, 'How bad do you want to win a stage in the Tour de France?' He said, 'Real bad,'" Armstrong recounted later. "I said, 'How fast can you go downhill?' and he said, 'I go downhill real fast.' He said, 'Can I do it?' And I said, 'Sure you can do it.' Then I told him, 'Run like you stole something, Floyd.'"
Landis zoomed away but was quickly caught by German Jan Ullrich, Armstrong's big rival. Armstrong laid chase, followed by Basso and Kloden. Together, Ullrich, Basso and Kloden had been the only riders able to stay with the two Americans on the last climb up the Col de la Croix Fry.
Hurtling toward the finish, the five riders eyed each other and jostled for position. Armstrong, distinctive in his overall leader's yellow jersey, put his sunglasses back on and took a couple of sips from his drink bottle.
Just after they passed under a blue inflatable arch marking 1 kilometer (1/2 mile) to go, Kloden made his move, spurting suddenly ahead to build a slight lead through the final corners.
But then, when it was almost too late, Armstrong hit the highest of his many gears. With a final glance over his shoulder and within sight of the line, he rocketed off in pursuit and found just enough speed to beat Kloden by a whisker.
"Something came over me and I said, 'OK. I have to go for it.' To get to win in the sprints is exciting," said Armstrong. "When I first started I thought, 'I'm not going to catch him ... But the finish line was far enough away that I made it through."
He dedicated his win to Landis, who led his boss up the grinding final climb. Landis' pace was so punishing that none but Basso, Kloden and Ullrich -- two, three, and four in the overall standings behind Armstrong -- could follow.
"He was the man of the day," Armstrong said of Landis. "In the Tour de France, to go to the front of the climb and ride tempo and end up with five guys is very hard to do."
"I really wanted him to win the stage," he added. "But it didn't work out that way."
When they hugged at the finish, still perched on their bikes, Landis told Armstrong: "I couldn't go any more."
The 28-year-old Landis, racing in his third Tour, finished last of the five in the sprint. Kloden was second, in the same time as Armstrong, with Ullrich third and Basso fourth, both one second back. Kloden is 5:11 adrift of Armstrong overall. Ullrich, the 1997 Tour champion and a five-time runner-up, is 8:08 back.
Armstrong has simply been in a different class.
He won the first Alpine stage on Tuesday, beating Basso, and rocketed to another overpowering win Wednesday in a time trial up the legendary ascent to the L'Alpe d'Huez ski resort.
He also beat Basso in the Pyrenees, having let the 26-year-old Italian win the first stage in his promising career a day earlier.
Since then, no more Mister Nice Guy.
"I've given gifts in the Tour de France, and very rarely has it ever come back to help me," said Armstrong. "This is the biggest bike race in the world and it means more to me than any bike race."
He will be a favorite to take a fifth stage win, a record for him in one Tour, in a time trial Saturday that will cement the top placings before Sunday's ride to Paris.
Apart from sprinters, who battle for the glory of winning on the crowd-packed Champs-Elysees, most riders treat that last stage as a lap of honor. Last year, Armstrong sipped champagne as he pedaled.
By picking up points on all but one of Thursday's climbs, French rider Richard Virenque guaranteed that he will win a record seventh mountain prize on Sunday.
Points are awarded to the first few riders over each climb, and Virenque has been gathering them up as the race has looped around France. Armstrong has not actively pursued that trophy, but still is second in the mountain rankings thanks to his climbing strengths.