Due to his superior ranking, Joo only entered the event at the third-round stage along with the other Asian powerhouses.
Yet he fell at the first hurdle to an opponent ranked 67 places lower in the ITTF rankings. Kim reeled off three successive games 11-7, 11-8 and 15-13 to seal a superb win.
'I did not have much control or confidence,' Joo said. 'I was very slow moving. The other player did not make many mistakes so I could not get the win.'
World number one Zhang Jike began his quest for gold in fine style – and then declared that the eventual winner would be Chinese.
Zhang, who is competing on the world's biggest stage for the first time, enters the men's Singles as favourite after winning the World Championships and World Cup last year.
He certainly began in style, wrapping up a straight-games victory against Bora Vang in just 31 minutes at the ExCeL Arena.
'The champion is going to be Chinese,' a confident Zhang said afterwards.
The other Chinese player in the event, Wang Hao, also got off to a winning start.
Wang is out to claim table tennis's biggest prize having had to settle for silver at Beijing 2008 and Athens 2004.
He was given occasional problems by Austria's 2003 world champion Werner Schlager, but eventually secured a 4-1 win.