David Ferrer believes five-time French Open champion Rafael Nadal is feeling the strain of the relentless pressure being created by red-hot Novak Djokovic.
Nadal struggled for over four hours to defeat John Isner in his first-round match on Tuesday, coming back from two sets to one down in his first five-setter at Roland Garros.
Djokovic, who won his opener in straight sets against Thiemo De Bakker on Monday, came into the French Open having defeated Nadal in the Madrid and Rome Masters claycort finals, as well as the Indian Wells and Miami deciders.
The Serb is also on a 40-match winning streak and is poised to take Nadal's world number one ranking by the end of the tournament.
"I saw part of Rafa's match and it was weird because he was not really there," said Nadal's Spanish Davis Cup team-mate Ferrer.
"And that's funny for Rafa. He was not really in the match. Then in the fourth and fifth he was controlling the match again.
"People say Rafa is no longer the player he used to be. I think he is still an excellent player. But just like anyone, he has moments when he doesn't play that well. He has a lot of pressure. Djokovic has put a lot of pressure on him."
Ferrer, the seventh seed, reached the third round on Wednesday with a 6-3, 6-4, 6-2 win over France's Julien Benneteau and will face Ukraine's Sergiy Stakhovsky for a place in the last 16.