Dominic Thiem's US Open campaign is over after he retired hurt in his last-16 clash with Juan Martin del Potro because of a knee injury.
The eighth seed was handed a tricky tie against the 2009 champion at Flushing Meadows, who took the opening set 6-3.
Thiem's movement appeared extremely hampered and he opted to call it a day trailing 3-2 in the second set.
Del Potro progresses to the quarter-finals of a grand slam for the first time since his run to the semi-finals of Wimbledon in 2013.
He will face the winner of the match between third seed Stan Wawrinka and Illya Marchenko in the last eight.