Pep Guardiola saw his side take the lead in the Premier League game with just two minutes on the clock when Raheem Sterling outjumped Arsenal defender Rob Holding and directed his header past Bernd Leno.
Manchester City pushed to extend their advantage, but Arsenal managed to stand firm and kept the visitors at bay; they could not break through at the other end however and suffered a defeat.
Pepe started in the game and clocked 73 minutes before being replaced by Emile Smith Rowe and admitted after the match he feels Arsenal have an issue concerning their concentration.
“We have concentration problems”, Pepe told French radio station RMC.
“We have to fix that.
“There was a goal and then nothing.”
Arsenal have lost eleven of their 25 Premier League games so far this season and have lost three of their last four league matches.
Mikel Arteta’s men played out a 1-1 draw against Benfica in the first leg of their last 32 Europa League tie last week and are due to host the Portuguese in the return fixture on Thursday.