The Three Lions had a lot of possession, but they did not get one shot on target and the German defence were barely troubled thanks to some industrious work in midfield from Lars and Sven Bender.
A second string Germany team shorn of the likes of Phillipp Lahm, Manuel Neuer and Mesut Ozil looked confident on the ball and had it not been for an excellent performance from Joe Hart, England could have been beaten by a much bigger margin.
Germany, who were unlucky to come away with only a draw in Italy last week, are the second-ranked team in the world and Mertesacker believes there are plenty of encouraging signs for Joachim Low's men ahead of the campaign in Brazil next year.
The Arsenal defender said: "We had a different squad for these two games and we showed overall that we have maybe 30 players who can be selected for the World Cup and that is a good sign.
"We are confident as a team. We were very stable in the 1-1 draw against Italy in defence. This is very positive.
"We have excellent team spirit as well as the large selection of good players.
"That's why I look optimistically to Brazil. Those things can make the difference in the summer. "
After spending the last two and a half seasons at Arsenal, Mertesacker was well prepared for the meeting at Wembley.
But he was taken aback at how poorly England had prepared for dealing with his threat from crosses.
"I was surprised that I was so free," said the 29-year-old, who stole ahead of Chris Smalling to turn the ball past Joe Hart just before half-time.
England were booed off the pitch just as they were following their 2-0 defeat to Chile last Friday.
Many viewed the results as proof that England cannot be regarded as serious contenders for the World Cup, but Mertesacker has told Roy Hodgson's squad they should not be too downbeat.
"There was a lot effort (from England)," Mertesacker said.
"They tried always but defensively we are quite strong at the moment and we didn't give them too much room so it was quite hard for them to come through.
"We did a lot to make sure it was difficult for them. Germany overall are always a threat and I think we showed that."
Borussia Dortmund will be cursing their luck after two of their players suffered injuries, ruling them out of this weekend's game against the team that beat them in the Champions League final last year - Bayern Munich.
The German Football Association said that defender Mats Hummels suffered an ankle injury that will keep him out until January.
Fellow Dortmund defender Marcel Schmelzer will be out for three weeks with a calf injury he sustained at Wembley.
Luckily for Bayern, defender Jerome Boateng has declared himself fit for Saturday despite coming off against England with a heel complaint.