Andy Schleck took the yellow jersey with two days to go as Pierre Rolland won a captivating 19th stage of the Tour de France on the Alpe d'Huez.
Schleck takes the overall lead from France's Thomas Voeckler, who lost more than two minutes on the final climb.
His brother, Frank, is 53 seconds behind him while Cadel Evans is just 57 seconds adrift ahead of Saturday's individual time trial in Grenoble.
Reigning champion Alberto Contador was third on the 109.5km trek from Modane.
His hopes of a fourth title came to an end on a day when one of the closest finishes in Tour history became a growing reality, with Andy Schleck and Australia's Evans - a time-trial specialist - now considered roughly equal favourites going into the deciding day.
Samuel Sanchez was crowned 2011 King of the Mountains after coming second on Friday behind talented young French rider Rolland.
Britain's sprint specialist Mark Cavendish retained the green jersey after finishing the last stage in the mountains in the same time as Spaniard Jose Joaquin Rojas, his nearest competitor.
Europcar's Rolland, 24, crossed the line after attacking near the end of the day's route, packed with thousands of wildly cheering cycling fans - some of whom bordered on the intrusive to the riders.
Leopard's Schleck made good on the promise he made on Thursday after missing out on the yellow jersey by only 15 seconds after winning the 18th stage following a daring solo attack on the Galibier pass.
He rode much of the stage 19 in a small group alongside Contador, but chose not to follow the Spanish rider when he attacked at the bottom of the punishing 13.8km Alpe d'Huez climb with its gruelling hairpins.
Rolland attacked as it drew to a tense finish, finally escaping Contador and Olympic champion Sanchez toward the top of the 6,100 foot final climb to take his first ever stage win.
"I grew up watching Lance Armstrong and Marco Pantani, watching how they climb the Alpe d'Huez," he said.
"Now I've won the Alpe d'Huez, it's going to take a minute to sink in."
Andy Schleck rode in 57 seconds behind Rolland in a group of six that included his brother and BMC's Evans, while Voeckler ended up three minutes and 21 seconds behind, dropping to fourth overall.
STAGE 19 RESULT
1. Pierre Rolland (France / Europcar) 3hrs 13mins 25secs"
2. Samuel Sanchez (Spain / Euskaltel) +14"
3. Alberto Contador (Spain / Saxo Bank) +23"
4. Peter Velits (Slovakia / HTC - Highroad) +57"
5. Cadel Evans (Australia / BMC Racing) same time
6. Thomas De Gendt (Belgium / Vacansoleil) same time
7. Damiano Cunego (Italy / Lampre) same time
8. Frank Schleck (Luxembourg / Leopard) same time
9. Andy Schleck (Luxembourg / Leopard) same time
10. Ryder Hesjedal (Canada / Garmin) +1:15"
1. Andy Schleck (Luxembourg/Leopard) 82hrs 48mins 43secs"
2. Frank Schleck (Luxembourg / Leopard) +53"
3. Cadel Evans (Australia / BMC Racing) +57"
4. Thomas Voeckler (France / Europcar) +2:10"
5. Damiano Cunego (Italy / Lampre) +3:31"
6. Alberto Contador (Spain / Saxo Bank) +3:55"
7. Samuel Sanchez (Spain / Euskaltel) +4:22"
8. Ivan Basso (Italy / Liquigas) +4:40"
9. Tom Danielson (U.S. / Garmin) +7:11"
10. Pierre Rolland (France / Europcar) +8:57"