While Del Potro is currently No. 145 in the ATP rankings, he’s no stranger to the big lights. In fact, it was Del Potro who defeated Djokovic in the bronze medal match of the London Games in 2012, keeping the Serbian from winning a medal.
Each of the two sets Sunday night required a tiebreaker, but Del Potro came out on top both times to secure a 7-6, 7-6 victory and advance to the second round.
Del Potro, 27, has been as high as No. 4 in the world and won the 2009 U.S. Open, but struggled with wrist injuries throughout his career. In 2014, he underwent surgery on his wrist and missed three Grand Slam tournaments, then missed all four tournaments in 2015 after continued pain eventually forced a second surgery.
The Argentinian finally returned to Grand Slam play this June when he advanced to the third round of Wimbledon, including a win over Stanislas Wawrinka.
But defeating Djokovic so soon after his return represents a significant upset. He’s the undisputed top tennis player in the world and has won six of the last nine Grand Slam tournaments. The last time Djokovic was bounced in the first round of a Grand Slam was more than 10 years ago in the 2006 Australian Open.
His Olympic success hasn’t matched his accolades in the ATP World Tour, though. Djokovic settled for a bronze medal in the 2008 Olympics after losing to Rafael Nadal in the semifinals and defeating James Blake in the bronze medal match. Then he lost in the semifinals again in 2012 with a loss in straight sets to Andy Murray, followed by a loss to Del Potro.
Del Potro, who had an interesting start to his Olympics after getting rescued by the Argentine handball team Sunday from a stuck elevator, will now advance to face Joao Sousa of Portugal on Monday. Djokovic will have to turn his attention to doubles. He’s paired with Nenad Zimonjic and the duo won its first round matchup Saturday.