The 20-time Grand Slam champion, lost to 14th seed Harris 6-4, 1-6, 6-4 in only his second match on the Washington hardcourts.

Nadal aggravated a foot injury in a three-set victory over American Jack Sock on Wednesday in his first match since losing a French Open semi-final to Novak Djokovic.

But the 35-year-old Spanish left-hander said after the match his sore left foot felt better than in his opening match even though he couldn't manage a victory.

Harris, ranked a career-best 50th in the world, booked a Friday quarter-final against Japan's Kei Nishikori after downing third-ranked Nadal, the highest-rated player he has ever beaten.