World No.1 and favourite to win the Olympic gold Novak Djokovic was stunned by bete noire Juan Martin del Potro, of Argentina, 7-6 (4), 7-6 (2) in the first round of tennis competitions at the Rio Olympics here.Djokovic, who had lost only four games so far this year, was on Sunday eliminated in his quest for the elusive Olympic gold, the only major tennis title so far missing from his incredible record, reports Xinhua news agency.Del Potro left the Olympic Tennis Center in high spirit, hoping the first-round victory will reactivate his career which has been lately ravaged by a string of wrist injuries.The 2009 US Open champion was haunted by chronic wrist injuries which forced him to step into the operating room several times and had him contemplating retirement from tennis.Del Potro, defeated the Serbian in the bronze medal play-off at the London 2012 Olympics, his last renowned victory.Djokovic won seven titles this year and currently holds twelve Grand Slam titles, including the 2016 editions of Roland Garros and Australia Open.Del Potro is set to face Portugal's Joao Sousa in the second round of Olympics competitions.