By Neil Maidment
The defending champion swept aside American Fish 6-3 6-3 5-7 6-4 on Court One and appeared to show no ill-effects from the foot injury he suffered in his defeat of Juan Martin del Potro but the Spaniard said only injections had been getting him through.
"My foot is not fine. But we are in quarter-finals of Wimbledon. It's an emergency, so I had to play," the world number one Nadal and top seed told reporters.
"I have pain on the foot. I cannot run in perfect conditions without sleep (anesthetic) in the foot. With the anesthetic there I don't feel the pain."
The top seed moved well on Court One, battering an inconsistent Fish with trademark groundstrokes and booming serves in the first two sets to take a commanding position.
"After the first two sets I probably played a little too defensive but I am happy to be in the semi-final, it is a dream for me," Nadal said.
Fish had dropped serve just once this year at Wimbledon but Nadal got off to a flyer, breaking him in the opening game before seizing another chance to take the first set comfortably.
Having seen off two break points early in the second set after a fizzing Fish forehand, Nadal's speed and accuracy soon took its toll on the American, who at times could only watch as the Spaniard racked up another set.
Six-times Wimbledon champion Roger Federer's shock departure had raised the biggest cheer of the day when displayed on the big screen but the Court One crowd finally had something else to shout about when Fish found his rhythm to steal the third set 7-5.
Fish, playing his first Wimbledon quarter-final, could not sustain his charge, though, handing Nadal a break in the third game before the Spaniard served out to seal a 19th successive win at the All England Club.
"I've served exceptionally well here this week in all four matches before this one. Maybe it's just the surroundings," Fish told reporters.
"I think I over-served at times, trying to go too hard, too quick. I know what I do wrong and try to correct it. Just never got a rhythm at all."
"He is playing really very well. He is a fantastic player, but after that I think he has a fantastic character. He is a very good guy and we play Playstation a lot off the court so we are friends," Nadal said.
(Editing by Ed Osmond)