CLUSES, France -- Lance Armstrong rode an unremarkable final mountain stage in the Tour de France on Thursday and finished far behind the winner.

Stage 17 -- At a glance

Stage An 88-mile stretch from Aime to Cluses, featuring four tough climbs. It was the last mountain stage of the Tour. Winner Italy's Dario Frigo, in 4 hours, 2 minutes, 27 seconds. How others fared Three-time champion Lance Armstrong retained the overall leader's yellow jersey despite finishing the stage in 24th place, 4:36 behind Frigo. Armstrong's lead over his nearest rival, Spain's Joseba Beloki, was unchanged at 5:06. Quote of the day "I sleep pretty good at night with the lead that we have.'' -- Armstrong on his overall lead, which should see him take a fourth straight title on Sunday. Next Stage A hilly 109.4-mile trek from Cluses to Bourg-en-Bresse.

In other words, it was a perfect day.

The leg from Aime to Cluses was the last chance for rivals to seriously challenge Armstrong. When it ended, no threat emerged, and the Texan retained an overall lead of 5 minutes, 6 seconds.

With such a huge advantage, Armstrong is almost certain to take a fourth straight title on Sunday.

"I sleep pretty good at night with the lead that we have,'' Armstrong said after the 17th stage, which he finished in 24th place, 4:36 behind winner Dario Frigo of Italy.

He certainly can afford to relax. The three remaining stages are much easier than the mountain legs, in which huge chunks of time can be won or lost.

Probably the biggest threat to Armstrong now is the possibility of illness or injury, particularly in Friday's hilly leg from Cluses to Bourg-en-Bresse.

However, Armstrong is also favored to win the last time trial on Saturday, and further extend his lead over second-placed Joseba Beloki of Spain.

Taking the 31-mile stage from Regnie-Durette to Macon would make up for one of Armstrong's few weak moments in the Tour, his loss in the ninth-stage time trial.

"It was not a good day,'' he said of the stage, which he finished in second place, 11 seconds behind Santiago Botero of Colombia. "I don't know why, I didn't feel great.''

The slip was soon forgotten as the Tour headed into the mountains.

Armstrong took the overall leader's yellow jersey by winning the first mountainous stage at La Mongie, in the Pyrenees. He opened a 1:12 lead over Beloki, which he more than doubled the next day by winning at the Plateau de Beille with a spectacular uphill sprint. He was so far ahead of Beloki that he had time to zip up his bright yellow jersey as he neared the line.

His lead grew to 4:21 after the climb up the formidable Mont Ventoux, and he added another 45 seconds in the most grueling stage of the entire race, Wednesday's trek from Les Deux-Alpes to La Plagne.

Armstrong's smooth performance in the mountains was helped by his rivals' lack of aggression.

"It's fair to say that there have not been many attacks,'' the U.S. Postal Service rider said. "But the event is challenging. The late mountain stages are real hard mentally.''

Armstrong won last year's Tour with a 6:44 advantage over Jan Ullrich of Germany. He could top that by winning the time trial, and round off what many consider his easiest victory.

Armstrong wouldn't say whether he found this Tour, one of the shortest ever, less challenging than previous years. But he said this year's U.S. Postal team was the best ever, and that his eight teammates made winning easier.

"The team has made it easier for me,'' he said. "To have guys always there in multiples, that makes life a lot easier.''

Frigo won Thursday's 88-mile stage in 4:02:27. He ducked in the final stretch to avoid the outstretched hand of a fan, who was trying to take a photograph.

Frigo was thrown out of last year's Giro d'Italia after a police raid revealed banned substances in some team hotel rooms, and he later drew a six-month doping ban. He rode for Fassa Bortolo at the time.