Djokovic, who won this year’s Australian and French Open titles, was the favourite to add Olympic gold to his 12 grand slam titles, and Del Potro was as surprised as anyone to see the Serb go out.
“I didn’t expect to beat Novak tonight,” said del Potro, who has been battling a wrist injury for much of the season.
“But I played an amazing match, my forehand worked great.”
Del Potro used his lethal forehand to stun the Serb with a powerful display to win 7-6(4) 7-6(2) in the biggest upset of the tennis tournament.
Earlier in the day, del Potro briefly got stuck in a malfunctioning lift but his luck improved against Djokovic, whom he also defeated in the bronze medal match at the London Games.
Del Potro has fallen outside the top 100 in the world rankings but showed flashes of the hard-hitting brilliance that helped him win the U.S. Open in 2009.