American rider Levi Leipheimer, a Discovery Channel teammate of Contador, won the 19th stage with a time of 1 hour, 2 minutes, 44 seconds in the 35-mile race against the clock from Cognac to Angouleme.
Contador lost most of his lead but still holds a 23-second advantage over Cadel Evans. Barring a crash or other mishap, the 24-year-old Spaniard is likely to bring home the yellow jersey today in the 20th and final stage - a 90.7-mile ride from Marcoussis to Paris' Champs-Elysees.
"I'm eager to go home and celebrate," said Contador, who was encouraged during the time trial by seven-time champion Lance Armstrong, who has ties to Discovery and was riding behind in a team car. "It wasn't an easy day."
The latest doping allegations didn't help.
French daily Le Monde, citing what it claimed was an investigation file it had access to, said Saturday that Contador's name, or initials, appeared in documents found at the apartment of Spanish doctor Eufemiano Fuentes, at the center of the Spanish doping probe known as Operation Puerto.
Contador said he was "sure" that he was not involved in the case, and insisted he was innocent. He said he would give a DNA sample to prove it if asked, but wouldn't offer one if it wasn't requested "because I'm innocent and I don't have to prove anything to anyone," he said.
STAGE 19 AT A GLANCE
Stage: Saturday's time trial took riders over 34.5 miles of flat roads from Cognac to Angouleme to the finish in Paris.
Winner: American rider Levi Leipheimer of the Discovery Channel team won in 1 hour, 2 minutes, 44 seconds.
Yellow Jersey: Alberto Contador of the Discovery Channel team kept the overall lead and the 24-year-old Spaniard will likely win the Tour today barring a crash. He leads Cadel Evans of Australia by 23 seconds.
Quote of the Day: "I don't think it's fair, but if I have to then I'll take it." - Contador when asked if he would take a blood test to prove that his DNA is not linked to the Operation Puerto blood-doping case.
Next stage: Today's 20th and final stage is a 90.7-mile ride starting from France's rugby center in Marcoussis and ending on the Champs-Elysees in Paris.