Juan Martin del Potro stunned a tearful Novak Djokovic in an emotional Olympics triumph Sunday as Venus Williams pondered the end of her four-gold Games odyssey. Del Potro, the 2009 US Open champion who was pushed to the brink of retirement by a series of wrist injuries, downed the top seed 7-6 (7/4), 7-6 (7/2). The giant Argentine had also defeated the 12-time major winner in the bronze medal match at the London Olympics in 2012. Both players embraced at the net and wept at the end of their center court duel played out in front of a raucous Argentine and Serb crowd. [caption id="attachment_75167" align="alignright" width="214"] Novak Djokovic of Serbia waves to the crowd after losing his match to Juan Martin Del Potro of Argentina. — Reuters[/caption]Del Potro, now ranked at 145 in the world after being No. 4 in 2010, said Sunday's win was more special than his victory in 2012. He had his first surgery in 2010 but more followed in 2014 and 2015 when he played just six events. "This victory is bigger than last time because I know how tough it was to come back from three surgeries," said the 27-year-old who unleashed more than 40 winners. Tonight I played one of the best matches of my career." Del Potro started the day by getting stuck in an elevator for 40 minutes at the athletes village where he had to be rescued by the Argentina handball team. But that inconvenience did not shake the Argentine out of his big-hitting stride as he set up a second-round clash with Portugal's Joao Sousa. "It's very sad and disappointing to go out of the tournament this early but I am glad that a good friend of mine, who has struggled with injuries, has won," said world number one Djokovic Meanwhile, four-time gold medallist Venus Williams was staring at the end of her 16-year, five-Olympics journey. Williams, 36, and sister Serena suffered their first ever defeat in women's doubles, a record which boasted 15 successive match wins and golds in Sydney in 2000, Beijing in 2008 and London four years ago. The 6-3, 6-4 loss to Czech pair Lucie Safarova and Barbora Strycova came just a day after Venus had been knocked out of the singles in what was her first opening round Olympics loss. At least, Serena is still alive in the singles as the defending champion had the perfect start in her quest for a fifth Games gold medal overall, defeating Australia's Daria Gavrilova 6-4, 6-2. Williams, sporting a patriotic Stars and Stripes hairband on centre court, will next face Alize Cornet, the Frenchwoman who defeated her three times in 2014, including at Wimbledon. London 2012 winner Andy Murray and 2008 Olympic champion Rafael Nadal breezed through in the men's singles. Wimbledon champion Murray, the second seed, clinched an eighth win in eight meetings against Serbia's Viktor Troicki, 6-3, 6-2. He next faces Argentina's Juan Monaco. There was one blot on the day for Murray as he and brother Jamie were knocked out of the men's doubles by Brazil's Andre Sa and Thomaz Bellucci. Nadal, playing his first match in two months, made the second round with a comfortable 6-2, 6-1 win over Federico Delbonis of Argentina. German second seed and Australian Open champion Angelique Kerber hit back from 2-5 down in the second set to defeat Mariana Duque-Marino of Colombia 6-3, 7-5. French Open champion Garbine Muguruza romped to a 6-2, 6-2 win over Romania's Andreea Mutu who was a late replacement for Jelena Jankovic who withdrew with a shoulder injury.