Sastre is likely to be pushed hard by Cadel Evans on Saturday
Carlos Sastre will enter Saturday's key 53km time-trial with a lead of one minute, 24 seconds following the 19th stage of the Tour de France on Friday.
The Spaniard finished among the peloton in the 165.5km Roanne to Montlucon stage, with Frank Schleck, Bernard Kohl and Cadel Evans in striking distance.
Sylvain Chavanel and Jeremy Roy split from the peloton at 80km and were never in trouble out in front.
And it was Chavanel who sprinted to victory ahead of his French compatriot.
As expected, none of the top five made any attacks during the 165.5km route from Roanne to Montluçon.
Sastre admitted he would not be taking any risks during Friday's relatively flat stage, a welcome break from the gruelling climbs earlier in the week, preferring to channel his energy for Saturday's crucial time-trial in Cerilly.
Silence-Lotto's Evans is set to attack the 53km course in Auvergne in an attempt to claw back the one minute 34 seconds deficit on Sastre before Sunday's final stage into the Champs-Élysées.
The lack of endeavour from the race contenders ensured the day belonged to Quick Step-bound Chavanel, who celebrated his first Tour stage win with tears after crossing the finishing line.
The 25-year-old French national time-trial champion had made countless breaks during this year's Tour, only to be overhauled in the final stages.
Chavanel made the break alongside Roy close to Charmeil, with both riders taking a five-minute lead at one stage.
The pair maintained their distance over the peloton right up until the finishing line, where a composed Chavanel outmanoeuvred Francaise de Jeux's Roy in the closing 500m.
"I was frustrated because I had been trying so hard and every time I had failed," said Chavanel.
"This year, I have overcome a barrier. It's the best gift I could offer Cofidis."
Team Columbia's Gerald Ciolek sprinted ahead of German compatriot Erik Zabel, both men finishing one minute 13 seconds behind the French pair.
Rabobank's Oscar Freire consolidated his position in the green jersey, maintaining his 42-point lead over rival Thor Hushovd, who failed to make a significant points gain during the race for third place.
Meanwhile former race leader Romain Feillu finished outside the cut-off time limit during Friday's stage.
The Agritubel rider, along with Germany's Fabian Wegmann and Spain's Juan Antonio Flecha, finished outside the 19 minutes 33 seconds limit.
Stage 19 results, Roanne to Montluçon (165.5km):
1. Sylvain Chavanel, (France/Cofidis), 3 hours 37 minutes 9 seconds
2. Jeremy Roy, (France/Francaise des Jeux) same time
3. Gerald Ciolek (Germany/Columbia) -1 minute 13 seconds
4. Erik Zabel (Germany/Milram) same time
5. Heinrich Haussler (Germany/Gerolsteiner) same time
6. Leonardo Duque (Colombia/Cofidis) same time
7. Filippo Pozzato (Italy/Liquigas) same time
8. Thor Hushovd (Norway/Credit Agricole) same time
9. Robert Foerster (Germany/Gerolsteiner) same time
10. Julian Dean (New Zealand/Garmin) same time
20. David Millar (GB/Garmin) same time
22. Cadel Evans (Australia/Silence-Lotto) same time
26. Christian Vande Velde (US/Garmin) same time
32. Denis Menchov (Russia/Rabobank) same time
38. Carlos Sastre (Spain/Team CSC) same time
46. Frank Schleck (Luxembourg/Team CSC) same time
48. Bernhard Kohl (Austria/Gerolsteiner) same time
Overall standings (after 19 stages):
1. Carlos Sastre (Spa/CSC) 82hrs 54min 36sec
2. Frank Schleck (Lux/CSC) +1min 24sec
3. Bernhard Kohl (Aut/GST) +1min 33sec
4. Cadel Evans (Aus/SIL) +1 min 34 sec
5. Denis Menchov (Rus/RAB) +2min 39sec
6. Christian Vandevelde (US/GAR) +4min 41sec
7. Alejandro Valverde (Spa/GCE) + 5min 35sec
8. Samuel Sanchez (Spa/EUS) + 5mins 52sec
9. Tadej Valjavec (Slovenia/AG2R) +8min 10sec
10. Vladimir Efimkin (Russia / AG2R ) +8min 24sec