Armstrong has repeatedly said he never used banned substances during his seven straight titles from 1999 to 2005, years after a dramatic comeback from his fight against testicular cancer.

Armstrong has been reunited with Johan Bruyneel, who was also his team manager during his Tour victories. Bruyneel says Contador is the man to beat, and has anointed the 26-year-old Spaniard as leader of the Astana squad.

Contador finished 31st in his first Tour in 2005, which was Armstrong's last. Contador has since won all three tours of France, Italy and Spain, one of only five riders to do so. This year, he's won two races, four stages and the Spanish time-trial championship.

Since Armstrong returned to competition this year, they have ridden together only once in a race — the Vuelta of Castilla and Leon in March — but Armstrong crashed out of it with a broken collarbone.

"Everybody has been waiting for the Tour to see this meeting of Lance and me, and it gives me added motivation — and pressure, too," Contador said.

Armstrong, once known as "Le Boss" of the Tour, can't be ruled out for victory. But his training regimen has been unorthodox in part because of his family duties, glitzy personal life and charitable work in the battle against cancer.

"What do I expect from him? Really, I don't know," Bruyneel said. "We are a bit lost. ... Alberto knows he's ready. Armstrong, we don't know."

As if cramming for a final exam, Armstrong spent Friday previewing the course but found time to keep in touch with his million-plus followers on Twitter.

"This place is going to be electric tomorrow," he tweeted.