Slovenia star Valter Birsa insists England are the best side in World Cup Group C but warned Fabio Capello's men that a shock could be on the cards.

England need a win over Slovenia in Port Elizabeth on Wednesday to assure themselves of a place in the last 16 in South Africa after drawing their opening two games.

For Slovenia's part, they need just a point to go through and were eight minutes away from reaching the knockout stages until the United States pegged them back to a 2-2 draw on Friday.

Auxerre playmaker Birsa believes his team need to be more strong mentally against England than they were against the USA, where they were well on top until Landon Donovan scored early in the second half to bring the Americans back into the game.

He told Press Association Sport: "We learned to make sure we don't finish before the game finishes.

"We must not allow ourselves to get it into our head that we have won the game.

"You have to be more clinical and wait for the possibility to score.

"In the first half we played well, we tried to score.

"In the second half we had 2-0 but the Americans changed their system.

"It should not have been so difficult but in our heads everything was going down, down, because they scored very quickly and that made it very difficult for us.

"We allowed too much space for them to play, but now we know what we must do against England.

"All the time you must try to play better. England are the most difficult team in this group, but you have seen already at this World Cup that the small teams can win against the big teams, so we know we have a possibility."

Slovenia coach Matjaz Kek may not face quite the same level of scrutiny as his England counterpart Capello, but he has called for his country's media to get behind the team.

He said: "There is too much that wastes our energy not related to the pitch, I hope that your attitude might improve because if this is not the case this may not have positive repercussions.

"Maybe you can come to our training camp and we can have a beer."