When all was said and done in Wednesday's Stage 17, the 26-year-old Spaniard further cemented his grip on the yellow jersey and Armstrong's ambitions for a podium spot were dealt a setback.
Frank Schleck and his younger brother Andy bumped the Texan down to fourth place from second as they broke away with Contador at the end of the 105-mile stage.
The elder Schleck won the stage.
Contador leads his closest challenger -- Andy Schleck -- by 2 minutes, 26 seconds, and seemingly only a major mishap could stop him from taking home the yellow shirt when the race ends Sunday.
Armstrong's challenge for a spot on the podium on the Champs-Elysees rides on the question: Can he regain ground in the time-trial today, and then hold on Saturday on the dreaded Mont Ventoux?
The Texan says a second-place finish is still within his reach.
"Yes, it's still my goal, I think it's possible," Armstrong said. "I just need to work hard on the time-trial tomorrow... We still have two big days."
Frank Schleck is 3:25 behind Contador. Armstrong, who crossed the finish 2:18 after the leading trio, now trails by 3:55 -- ending any hope that he will win the Tour, barring a miracle.
WINNER: Frank Schleck of Luxembourg, ahead of race leader Alberto Contador and brother Andy Schleck. They broke away in the Col de la Colombiere after a move from Contador.
YELLOW JERSEY: Contador, the 2007 winner, now leads Andy Schleck by 2 minutes and 26 seconds. Frank Schleck is in third place, 3 minutes and 25 seconds behind. Lance Armstrong dropped to fourth overall, 3:55 behind his Astana teammate.
QUOTE OF THE DAY: "Getting lots of question why AC attacked and dropped (teammate Andreas) Kloeden. I still haven't figured it out either. Oh well" -- Armstrong on his Twitter feed, about Contador's move in Wednesday's final ascent.
NEXT STAGE: Today's stage is a 25.2-mile individual time-trial around the Annecy Lake. The course is mainly flat but features a slight uphill 7.5 miles away from the finish.