By Alastair Himmer
A leg injury suffered early in the match made the world number one's quest to become only the third man, and first since 1969, to achieve the iron man feat almost impossible.
"It's a difficult day for me," a glum-looking Nadal told reporters. "Obviously I didn't feel at my best, I had a problem at the beginning and after that the match was almost over.
"I hate retiring. I hated that last year and I didn't want to repeat that," added Nadal, whose 2010 challenge ended at the same stage when he retired hurt against Britain's Andy Murray.
"I prefer we don't talk too much about the injury. First thing, I don't know (what it is) and also out of respect for the winner.
"It seems like I always have a problem when I lose, I don't want to have that image."
The nine-times grand slam champion returned to the court with his thigh strapped after visiting the trainer, but was clearly in pain, wincing and muttering to his uncle and coach Toni.
Seventh seed Ferrer, who had lost 11 of his previous 14 meetings with Nadal, including the last seven, showed no mercy, ripping shots to all corners to keep the pressure on.
Moments later, he was choking back tears after Ferrer tore into a 3-0 lead in the third but he battled like a true champion to get on the board, even forcing a break point at 4-2 down.
However, Ferrer kept his nerve and closed out the quarter-final with another big forehand after two hours and 33 minutes.
"David is having a fantastic tournament and if he keeps playing like that he has a great chance," said Nadal. "I would love him to win the tournament. He's a fantastic person and a very good friend."
Ferrer had mixed feelings after advancing to only a semi-final against fifth seed Murray, last year's runner-up.
"It's not easy because Rafa is a gentleman and he played with injury as we are friendly," said Ferrer, unbeaten in 2011 after winning a warm-up tournament in Auckland.
"I played aggressive, but if Rafael was not injured, I wouldn't have won in three sets," he added after reaching his second grand slam semi-final, and first since the 2007 U.S. Open, a run which also included a win over Nadal.
"It's one big (achievement) for me but it's not a victory really. These last two weeks have been unbelievable. I will try to do my best to win a slam.
"But Rafa can still win the next four grand slams. He's one of the top three players in history."
(Editing by Martyn Herman)