Sainz drove the 183 miles from the port city of Valparaiso to La Serena, on the rim of the Atacama desert, in 3 hours, 47 minutes, 19 seconds. Volkswagen teammate Dieter Depping was 4 minutes, 2 seconds back and Mark Miller of the United States was third, another 10 seconds back.
Miller was in third in the overall standings and NASCAR star Robby Gordon was fifth in a Hummer.
Sainz said the outcome of the race is far from decided.
"As long as the rally isn't over, then nothing is certain," he said. "I'm keeping my fingers crossed and I hope that we'll carry on being as successful as we have been today."
In the motorcycle competition, Cyril Despres of France won in 4:09:28 for his 18th career stage victory, with overall leader Marc Coma of Spain 1:49 back in second. Chile's Francisco Lopez was third, 2:56 back.
Monday's ninth stage will take the drivers through the sand dunes of the Atacama desert to Copiapo.
This is the first time the race is being staged in South America after being moved from African due to the threat of terrorism.
Chilean President Michelle Bachelet spoke during a visit to the drivers' camp in Valparaiso on Saturday and told organizers and drivers that her government will work to have the rally stay in South America next year.
Espanyol Hold Real Betis
Peterhansel abandons Dakar; Sainz back in front
Sainz regains lead of Dakar Rally with stage win
