The defending champion managed his first two sets with ease, winning 6-3 6-3, but failed to break Fish's serve in the third, eventually conceding the set 5-7. He secured his place in the semi with a 6-4 win in the fourth set.
Speaking afterwards, Nadal admitted he had made "a few mistakes" and "lost a bit of the intensity" in the third set but said he was "happy" with his overall performance. He also confirmed that his suspected foot injury was "nothing important" and that he would be "fine" for the upcoming fixture against Andy Murray in Friday's semi.
Of Murray, Nadal added: "He's playing really well here. He's always a pleasure to play against - he's not only a fantastic player but he has a fantastic character too."