Ferrero won at Roland Garros two years ago but Nadal showed why he is the reigning French Open champion as he out-hit and out-ran his opponent, forcing too many errors out of Ferrero.
"I played good on the important points," said Nadal, who took his third win in as many meetings with Ferrero. "You look at the scoreboard and it says 6-3, 6-3, but the match was very tough."
The 19-year-old Mallorcan, who is bidding to become the first player since Thomas Muster in 1996 to win seven claycourt titles in one season, added: "It was my best match in the tournament so far. I played with good determination."
Ferrero threw everything he could at Nadal in the second set but failed to convert break points while ahead at 1-0 and 2-1 and when Nadal served to love for 3-3 the Valencian ran out of gas. Nadal broke twice more to seal the match.
Robredo disposed of Russian sixth seed Mikhail Youzhny 3-6, 6-4, 6-3.
Czech Jiri Vanek moved into the last four by beating Spain's Oscar Hernandez 6-4, 6-2. He will face either compatriot Tomas Berdych or Argentina's Mariano Zabaleta, the winner here in 2003 and 2004.
