By Julien Pretot
Nadal, whose four-year domination at Roland Garros was ended exactly a year ago by Sweden's Robin Soderling, was pushed hard by the 22-year-old after dominating the first set but the outcome was never seriously in doubt.
The Spanish world number two had his serve broken four times during the two hour 33 minute contest on a packed Court Philippe Chatrier but always found a stinging response to deflate the 24th seed.
The claycourt master would not be drawn into talks on a possible dream final against holder Roger Federer, although he has been playing some impressive tennis so far.
"I played probably my best match today in the tournament," Nadal, who won the Monte Carlo, Madrid and Rome claycourt Masters tournaments on his way to Paris, told reporters.
"I am in the quarter-finals. I am very happy to be here, and you will have Nadal v Almagro, sure," he added.
Nadal, who slipped on a banana skin last year against Soderling, remained cautious and was already looking for improvement.
"I wanted to have longer and deeper shots. I want to improve this. Sometimes, these details are such that the opponent could take this opportunity so as to dominate the game."
(Editing by Miles Evans)