Rafael Nadal remains the favourite to win the US Open and move within one on Roger Federer's tally of 20 Grand Slams after a hard-fought quarter-final win over Diego Schwartzman.
Spanish second seed Nadal won 6-4 7-5 6-2 against the Argentine 20th seed.
But he was made to work as Schwartzman twice rallied from four-game deficits before succumbing on a stuffy Ashe.
Nadal, 33, will play Italy's 24th seed Marco Berrettini in Friday's semi-finals.
Three of the men's semi-finalists - Berrettini, Grigor Dimitrov and Daniil Medvedev - have never played in a Grand Slam final.