Manchester City boss Manuel Pellegrini was left frustrated as he saw his Manchester City side suffer their second 2-1 home defeat of the week.
The Citizens were expected to bounce back after Tuesday's defeat against Juventus in the Champions League.
But they disappointed once again as they lost 2-1 against West Ham United.
"I'm frustrated as they were three very important points at home," Pellegrini told reporters.
"They won their two away games before tonight against Arsenal and Liverpool so I knew it would not be easy but we conceded two easy goals and that allowed them to be in front.
"In the last two games we didn't play with the concentration or intensity we had shown in the first five games.
"We did exactly the same today as against Juventus – they had two chances in the whole game. We must be more concentrated.
"To win the game you must score, and we didn't score. We played very well in the second half, though not in the first. We were not the aggressive team we need to be at home.
"We corrected those things, played very well, created a lot of chances but didn't score. We were under pressure, falling two goals behind. It is always difficult to play against any Premier League team - everyone has very good players."