Sandy Casar won Friday's Stage 18, covering the 132-mile route from Cahors to Angoulme in 5 hours, 13 minutes and 31 seconds, winning a sprint to the wire that allowed him to edge three riders for his first Tour de France stage victory.
Axel Merckx, Laurent Lefevre and Michael Boogerd were each timed 1 second behind Casar.
Contador finished Friday's stage in 16th place, two slots and 3 seconds behind Cadel Evans, who is in second place overall. Contador owns a 1:50 lead on Contador and is 2:49 ahead of third-place Levi Leipheimer.
This year's Tour de France of more than 2,200 miles could well be decided in Saturday's 34.7-mile time trial from Cognac to Angouleme. The tour wraps up Sunday with a 91-mile run from Marcoussis to Paris, with the final miles completed on the Champs-Elysees.