Germany forward Thomas Muller said his team are under significant pressure following their 1-0 loss to Mexico on Sunday.

The defeat was Germany's first in a World Cup opener since 1982, when they were beaten 2-1 by Algeria but still made it to the final of the tournament held in Spain.

Fielding eight players from their 2014 winning side, Germany showed little resistance as Mexico only missed out on winning by a greater margin by wasting several counter attacks in the last 20 minutes.

"It was a bit like in our friendly against Saudi Arabia -- we allow the opponent too much space to counter when we have possession," Muller, referring to the 2-1 win on June 8, told FIFA's website. "And Mexico did a very good job. They relied on their defending and then tried to immediately go into the transition play.

"All in all, we talk about the same issues in the past games. And we try to stop, but if we continue to have as much possession, the danger will be high that if you lose the ball, the opponent will get their chances."

Germany will play Sweden on Saturday and must win to maintain their chances of winning the group.

"The pressure is extreme," Muller said. "There's no room for any more slip-ups. It feels like the knockout stages have begun. We did not want this situation. We wanted to avoid it. We must handle it now.

"The belief is still there, but we are [far] from being euphoric."

Thomas Muller knows Germany need to win their next two games to advance beyond the group stages. Patrik Stollarz/AFP/Getty Images

Marco Reus, meanwhile, told reporters he found out during Germany's pre-World Cup training camp in Italy that he would not start the game against Mexico.

Low, who told Reus he would "play in the important matches," handed the injury prone Borussia Dortmund midfielder his World Cup debut in the 60th minute.

"We'd like to think that it will be a long tournament," Reus said.

"Sure, that match today was also important, but we've got a big squad and everyone's needed, and that's why it was agreed upon that way."