Playing a slick and fast passing game, the South Koreans comfortably beat Greece 2-0, a result that could prove decisive for the Asian team, unbeaten in qualifying and semi-finalists in 2002, as they seek a spot in the second round.
Group favourites Argentina beat Nigeria 1-0 in their opening game, and the Koreans said the South Americans would be hard to overcome in Thursday's match at the Soccer City stadium in Johannesburg.
"Argentina is a very strong team, but we have to be confident, watch this game and see which tactics they are going to use. It doesn't matter if there is a favourite, because in soccer the unexpected can happen," said coach Huh Jung-moo, the national team's first local coach since the 1998 finals.
South Korea beat Greece with quick breaks and neat passing play that left their opponents outnumbered at the back, but will be hard pressed if Argentina's Lionel Messi's stellar performance on Saturday is anything to go by.
Although he did not score, Messi, the world player of the year, peppered the Nigerian goal with shots and tormented the Africans with his jinking runs.
Only some excellent saves by Nigerian goalkeeper Vincent Enyeama avoided a much bigger defeat.
Korean Cha Du-ri said such was the threat posed by Argentina, the team were targeting the match against Nigeria in Durban on June 22 as being crucial to their hopes of advancing.
"Argentina have world class players ... anything can happen, but realistically, we are focusing on Nigeria. The last game will decide who can advance," said Germany-based Cha, who in an energetic duo with Park Chu-young proved a handful for the Greek defence.
South Korea have dominated the Asian game and arrived in South Africa determined to reverse their mediocre World Cup form with a team built around their more experienced players based in Germany, England, Russia, France and Scotland.
What they lack in size, the Koreans make up for in the fitness and industriousness exemplified by captain Park Ji-sung, nicknamed "Three-lunged Park" for his astounding stamina, who scored in the opener along with Lee Jung-soo.
The Koreans defended solidly against the aerial threat of the Greek players and their speed, discipline and slick performance won them the first game.
