Cape Town - Per Mertesacker says Arsenal's defeat at Swansea was a result of not playing "serious football" for a full 90 minutes.
Alexis Sanchez 12th goal of the season gave the Gunners a second-half advantage but Gylfi Sigurdsson and Bafetimbi Gomis struck inside three minutes to turn the game on its head.
Arsenal were disciplined and organised for much of Sunday's game but Mertesacker admits they let their standards slip after taking the lead.
"The game was completely in our hands, especially in the second half when we scored," he said on arsenal.com.
"Then we have to play serious football and not lose the ball but they got us on the break, and that’s completely unbelievable in our situation.
"We have to play simple, even if we are 1-0 up - even more then. We played through the middle… but we need to keep possession and keep patient, something that we did all the way through until the 60th minute and we had the game in our hands completely. That’s what I mean by serious football.
"When you get such a result [like against Anderlecht] normally you come back quickly and after such a setback normally we bounce back immediately. Today that was not the game and we have to take the break now really seriously and work hard on the issues."
Mertesacker is convinced that Arsenal can fix their problems - if they learn their lessons quickly.
"We have the potential and we have to extend 60 minutes [of performance] to 90 minutes, that’s not a big issue.
"We played our game for 60 minutes with patience, seriously and they didn’t have a proper chance. Then we scored and we thought we didn’t need to keep possession or patience, and then we struggled. That was our fault and we did the same on Wednesday. We have to think about it quickly.
"We have good ideas on how we can extend the good 60 minutes into 90 minutes. It’s absolutely necessary in the next couple of weeks. We struggled a bit but we have great potential and you can see that.
"Now we have some time to think about the few issues that cause trouble because we made mistakes in areas we have to avoid."