Juan Martin del Potro became the lowest ranked man since 1991 to reach the US Open quarter-finals when opponent Dominic Thiem retired from their last-16 tie through injury on Monday.
The 142nd-ranked Argentine was leading 6-3, 3-2 when the eighth-seeded Austrian quit with a knee injury.
Del Potro, the 2009 champion, faces either Stan Wawrinka or Illya Marchenko for a semi-final place.
Jimmy Connors was ranked 174 when he went on to the US Open semi-finals in 1991.
Fifth-seeded Romanian Simona Halep advanced to the quarter-finals of the US Open for the second straight year on Monday with a 6-2, 7-5 victory over Spain’s Carla Suarez Navarro.
Halep, a former French Open finalist who has won three WTA titles in 2016, could find Serena Williams waiting for her in the last eight, with the world number one taking on 52nd-ranked Kazakh Yaroslava Shvedova later Monday.