The former champion was in devastating form at Flushing Meadows, losing just four games on his way to sealing a semi-final clash with Richard Gasquet.
Despite describing his victory over Robredo as his "best" of the tournament, the 27-year-old said that he still needs time on the practice court before encountering the Frenchman.
"I think I played my best match of the US Open this year," Nadal said in his on-court interview. "It gives me a lot of positive energy.
"I'll play a little bit tomorrow. I need it. Richard is playing a great tournament and it's great to see him in the semi-finals."