"This gives me reasons to think I'm on the right way," said Nadal, the former top-ranked player in the world who left the tennis circuit following last year's Wimbledon Championships to have knee surgery.
Chardy, a semifinalist in this event a year ago, advanced with a 6-2, 6-3 decision over Paolo Lorenzi.
The other semifinal will match Horacio Zeballos and Carlos Berlocq. Zeballos outlasted Albert Ramos in the quarterfinals 6-1, 5-7, 7-6 (8-6) and Berlocq moved on without having to play when Guillaume Rufin withdrew with an abdominal strain.
Nadal is seeking the 51st tournament title of his career. This spring, he will attempt to win the French Open for the eighth time in nine tries.