Per Mertesacker has admitted that Arsenal must "work hard" to cut out mistakes after seeing his side fail to hold onto a lead once more to fall to their second defeat of the Premier League season.
The Gunners led Swansea City 1-0 heading into the final 15 minutes at the Liberty Stadium courtesy of Alexis Sanchez's strike, but two goals in quick succession from Gylfi Sigurdsson and Bafetimbi Gomis saw the hosts come out on top.
Having also seen his side throw away a three-goal lead against Anderlecht in the Champions League in midweek, Mertesacker slammed his teammates for failing to play "serious football".
"The game was completely in our hands," the former Germany international told Sky Sports News. "But then we have to play serious football and not make mistakes.
"Anderlecht came back at 3-0 and Swansea came back today from one goal. We have potential, but unless we play that serious football any team will punish us.
"We have to play simple. We think we can do some difficult things, but we need to keep possession. After such a setback as Anderlecht we normally bounce back straight away, but we didn't. We need to work hard on the issues now."
Today's defeat leaves Arsenal in sixth place in the table following their second worst start to a Premier League season.
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