Juan Martin del Potro came back from two sets down and saved two match points to beat sixth seed Dominic Thiem in a raucous US Open classic.
The 24th seed, cheered on by a large Argentine contingent on the Grandstand court, won 1-6 2-6 6-1 7-6 (7-1) 6-4.
Despite feeling ill and requiring treatment, he came through in three hours and 35 minutes to set up a quarter-final against Roger Federer.
The Swiss third seed beat Germany's Philipp Kohlschreiber 6-4 6-2 7-5.
Federer, 36, struggled with a back injury in the build-up to the tournament and left the court after the second set for a medical timeout.