Both host nations are under pressure to perform on home turf.
South Korea have the best qualifying record in Asia - these are their fifth successive finals - but they have yet to win a single game.
Japan have the benefit of an open group which pits them against Russia, Tunisia and Belgium.
Reigning Asian champions, they finished runners-up to France in the Confederations Cup and have had some success with their policy of playing more established footballing powers.
Senegal get their first ever finals underway with the most difficult of tasks - a clash with world champions France.
But they are not quite the huge underdogs one might imagine.
Almost the entire squad play their domestic football in France, and that experience showed as they reached the final of this year's African Nations Cup.
Fired by the goals of El Hadju Diouf and the midfield skills of Khalilou Fadiga and Liverpool-bound Salif Diao, they have a real chance to progress if Uruguay and Denmark can be dealt with.
The United States do not have to do a great deal to improve on their showing at France 98 - they finished with the worst record of any side in the finals.