Del Potro lowest ranked US Open quarterfinalist in 25 years

Argentine Del Potro was leading 6-3, 3-2 when the eighth-seeded Austrian retired with a right knee injury having received a medical timeout just moments earlier.

Del Potro, Argentina, tennis player, US Open Rio Olympics

Del Potro, the 2009 champion who was pushed to the brink of retirement earlier this year after undergoing three surgeries on his left wrist, will face either Stan Wawrinka or Illya Marchenko for a semifinal place. ( File photo)   -  Getty Images

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.

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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 semifinals of Wimbledon in 2013.

He will face the winner of the match between third seed Stan Wawrinka and Illya Marchenko in the last eight.