Nadal, who lost to Novak Djokovic in the final at Flushing Meadows earlier this week, hammered Richard Gasquet 6-3 6-0 6-1 in the opening rubber.
And David Ferrer made equally short work of Gilles Simon, wrapping up a 6-1 6-4 6-1 success to put Spain on the verge of a place in the final.
"It's very painful to watch your players suffer against such a good team," France captain Guy Forget said on daviscup.com. "They played all right, but to beat Spain in Spain you have to play great."
Nadal broke seven times and fired 33 winners in a one-sided match with Gasquet in Cordoba.
The big-hitting left-hander broke twice to take the first set 6-3, hitting winners off either flank and dropping only six points on serve.
The Mallorca native then powered through the second in the most dominant fashion imaginable, never dropping a point on serve and taking 21 of 34 when receiving as he broke three times to win the set 6-0.
The pattern continued into the third as a booming forehand winner earned Nadal a break in Gasquet's first service game. Two more such shots earned him break points next time around, but Gasquet held firm and won his first game since the opening set.
A second break followed for Nadal in game six, though, and he served out to seal victory in two hours seven minutes.
"I was serving well, especially in the opening two sets, and that gave me a lot of composure," Nadal was quoted by atpworldtour.com telling Spanish television. "The effort was positive, [but] if the game had dragged on, it could have been tough for me."
World number five Ferrer swept side Simon in two hours eight minutes.
Spain can now wrap up victory in the doubles on Saturday when Feliciano Lopez and Fernando Verdasco take on Michael Llodra and Jo-Wilfried Tsonga.
Argentina, runners-up in 2006 and 2008, also seized control of their last-four clash in Belgrade with defending champions Serbia, who were without world number one Djokovic.
The newly-crowned US Open champion declared himself too fatigued to take part after a gruelling run in New York.
"I'm close to the end of my energy," he said. "I'm not in perfect condition physically, I know that. If the match stays longer it will be very difficult for me."
Djokovic's absence was keenly felt as David Nalbandian beat Viktor Troicki 6-4 4-6 6-2 6-3 in the opening rubber and Juan Martin Del Potro made it 2-0 with a 7-5 6-3 6-4 over Janko Tipsarevic.
Troicki looked to have got himself back in the match when he broke in the ninth game of the second set to level the scores.
But former world number three Nalbandian turned on the style in the third, hitting a flurry of winners, and did not let up in the fourth to claim victory in two hours 51 minutes.
Del Potro broke once in each set to close out victory in two hours 31 minutes.