Per Mertesacker says Arsenal must heed the lessons of back-to-back collapses against Anderlecht and Swansea and start playing "serious football" to get their season back on track.
It was groundhog day for Arsenal and their supporters at the Liberty Stadium on Sunday afternoon following Alexis Sanchez's 63rd minute goal - the Chilean's 12th of the season and sixth in his last four games - looked like claiming three Barclays Premier League points.
Gylfi Sigurdsson and Bafetimbi Gomis struck late on to give Swansea a 2-1 victory and leave Arsene Wenger's side with another hangover just five days after they had wasted a 3-0 Champions League lead against Anderlecht to draw 3-3 at the Emirates Stadium.
German defender Mertesacker said Arsenal's second Premier League defeat of the season was a result of letting their standards slip for the second time in the space of a week.
"The game was completely in our hands, especially in the second half when we scored," Mertesacker said.
"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.
"But that was not the game and we have to take the (international) break now really seriously and work hard on the issues."
Mertesacker said Arsenal can remedy their problems if they learn their lessons quickly and turn 60-minute performances into 90-minute displays.
"We played our game for 60 minutes with patience, seriously, and they didn't have a proper chance," Mertesacker said.
"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 against Anderlecht. We have to think about it quickly."