Second seed Nadal -- a winner at Flushing Meadows in 2010, 2013 and 2017 -- beat a spirited Schwartzman for the eighth time in as many meetings in a match that finished early Thursday morning.
Schwartzman put up firm resistance against Nadal and twice fought back from double-break deficits in the first two sets, but the Spaniard found another gear at crucial moments to secure an eighth semi-final berth in New York.
“Straight sets but big challenges especially after the first two sets, having 4-0 and 5-1 and losing both breaks in a row, but I know how good he is when he’s confident,” Nadal said.
“I’m so happy how I accepted the situation and challenge and kept going, point after point. Here I am in the semi-finals. I’m super happy, it means everything.”
Nadal also played down concerns over his left forearm as he received treatment early in the third set.
“Physically I am fine. Today was a very heavy day, big humidity out there. I’m this kind of player who sweats a little, but sometimes under these conditions it’s tough,” he said.
Nadal is the only former major champion left in the men’s field following the elimination of Roger Federer and Novak Djokovic, leaving him as the clear frontrunner in his pursuit of a 19th major title.