Sami Khedira, who has successfully replaced Michael Ballack in Germany's midfield, is wary of a backlash from Serbia in Friday's World Cup clash.

Serbia went down 1-0 to Ghana in their opening match in Group D last Sunday and next face high-flying Germany, who hammered Australia 4-0 the same day, in Port Elizabeth needing a win to remain in the tournament.

Former Chelsea star Ballack is out of the World Cup with an ankle injury, but his replacement Khedira has already forged a partnership alongside Bastian Schweinsteiger in midfield and will face the Serbs.

The Germans produced arguably the best performance of the World Cup so far by hammering the Socceroos, but Khedira says the challenge is now to tame Serbia and maintain the momentum generated by the opening win.

"We have to be ready to run against Serbia and display the same brand of football we produced against Australia," said the 21-year-old.

"This game is no foregone conclusion, the Serbs will be very fired up and dying to get something from this match."

Khedira, who holds a Tunisian passport, is among the next generation of talented German footballers like Brazil-born striker Cacau and second-generation Turk Mesut Ozil, who have caught the world's attention here.

While the multi-cultural Germans are now seen as the team to beat here after their dynamic display, Khedira said the team are just focused on Serbia.

"The success won't spoil us in the least, we have our feet on the ground," he said.

"We know we have to practice and train hard, what is said and written about is not our concern, we are just interested in the Serbia game."

The Germany camp are extra wary of the Serbians having learned the lessons of Euro 2008.

Two years ago at the Austria and Switzerland-hosted tournament, Germany beat Poland in their opening game, only to lose to Croatia in their next group match before going on to reach the final.

Assistant coach Hansi Flick says the same mistake will not be made again.

"This team is entirely different from the Euro 2008 squad," he said.

"They are a young team, who are only looking forward, never back.

"They are very focused and need no reminding, so we are on a good track."

Flick said the Germans are concerned about the threat of imposing Serbian striker Nikola Zigic, who at 2.02 metres tall has the height to power his headers down into the path of his fellow Serbian attackers.

Bremen's Per Mertesacker will be charged with the task of containing Birmingham City's Zigic and the German has experience of the role having marshalled giant Jan Koller of the Czech Republic in previous internationals.

"(Per) Mertesacker is tall as well and he has already played that role against Koller, he had no problems," said Flick.

Serbia have plenty of Premier League talent in their squad with their defence led by Chelsea's Branislav Ivanovic and Manchester United's Nemanja Vidic.

"Serbia will be a higher calibre side than Australia," said Flick.

"With Vidic and Ivanovic they have very experienced players who are strong and compact in defence. We will have to concentrate for the full 90 minutes."

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