Greece coach Otto Rehhagel has warned his players they cannot afford another lapse in concentration if they are to keep their World Cup dreams alive.

The Greeks opened their Group B campaign with a 2-0 defeat to South Korea in Port Elizabeth on Saturday, and head into Thursday's clash with Nigeria and are still waiting to score the first World Cup finals goal in their history after four successive defeats.

Rehhagel admits their hopes of changing that record at the weekend were blown out of the water inside seven minutes when they failed to pick up Korean defender Lee Jung-soo as he met Ki Sung-yueng's free-kick to open the scoring.

The 71-year-old German said: "Basically, we played into our opponents' hands from the seventh minute.

"There were 18 people in the penalty area and if the ball is hit hard across it, anything can happen.

"The defenders failed to head it away and South Korea took full advantage.

"Having said that, you cannot always prevent those situations."

Rehhagel, whose squad is now preparing for the Nigeria game in Durban, knows there is little margin for error with Argentina awaiting them in the final group game.

He said: "We have got to examine the last match very carefully and then we will try to improve in a very sober manner and learn our lessons.

"But we are coming up against the strongest teams in the group now."