RIO DE JANEIRO – Serbia’s Novak Djokovic, the current world number one in men’s tennis, has been knocked out of the Olympic tournament in Rio de Janeiro after losing 7-6 (7-4), 7-6 (7-2) to Argentine Juan Martin del Potro in the opening round early Monday.

World number 141 Del Potro won after nearly two and a half hours of play in a performance reminiscent of his best, injury-free days, conceding no break points to Djokovic.

It was their 15th encounter and just the fourth victory for Del Potro – albeit a very painful one for Djokovic, like the one in the bronze medal match at the London Olympics.

Del Potro will next face Portugal’s Joao Sousa, while Djokovic will continue his doubles campaign with Nenad Zimonjic.