Sastre was not pushed by Cadel Evans in the stage 20 time-trial
Spaniard Carlos Sastre is heading towards his first Tour de France win after his rivals failed to gain ground in Saturday's key 53km time-trial.
Sastre led by 84 seconds going into the stage but main rival Cadel Evans could only close the gap to 65 seconds with just Sunday's final stage remaining.
Stefan Schumacher won the stage by 21 seconds and Britain's David Millar was fifth while Bernhard Kohl is now third.
Frank Schleck fell from second to sixth overall after a disappointing ride.
Gerolsteiner's Schumacher, who also won the first time-trial of the 2008 Tour, clocked a best time of one hour, three minutes and 50 seconds to beat Swiss Fabian Cancellara by 21 seconds, with Luxembourg's Kim Kirchen coming home third.
But, on the most important day of the Tour so far, all eyes were on the battle between leader Sastre and overall favourite Evans and their individual races against the clock.
On the last 15 km, Sastre was riding as fast as Fabian Cancellara
Bjarne Riis CSC team manager
Widely expected to overcome a one minute, 34 seconds deficit to leapfrog Sastre, Evans failed to set the pace needed through intermediate checkpoints between Cerilly and Saint-Amand-Montrond and finished seventh, beating the Spaniard by just 29 seconds.
The scene was set for one of the closest Tour finishes in history but Sunday's 21st and final stage - a 143km ride from Etampes to the Champs-Elysees - is now likely to be a ceremonial ride for Sastre.
"I was calm this morning, I knew it was an opportunity of a lifetime for me," said Sastre. "The dream has come true.
"I was feeling better and better on this Tour. I have a good capacity to recuperate from my efforts."
Sastre, who took the yellow jersey courtesy of a bold attack on the ascent to Alpe d'Huez, leads Evans by an apparently insurmountable minute and five seconds, while Gerolsteiner's Austrian climber Bernhard Kohl is in third place, one minute, 20 seconds off the pace.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.