Chelsea boss Mauricio Pochettino admitted that his team had many issues he must solve.
The Blues had started their season positively, drawing 1-1 with Liverpool at Stamford Bridge.
However, their second league game of the campaign saw them crash to a 3-1 loss to West Ham United, despite having an extra man for roughly half an hour of second half action.
Post-game, Pochettino told reporters: "I don't believe we can call it a mentality thing [the loss]. I think today the result doesn't reflect the performance. In football, we need to accept that these kind of situations happen. I think the first-half was really good.
"Only disappointed and the players are really disappointed in the way we conceded the first goal because we start the game knowing West Ham are so, so dangerous in set-pieces, corners. We conceded a few corners and then we conceded the goal. That is a little bit disappointing.
"I was really upset at half-time about that. I think the players will agree and feel the same and then I think also we did really well in the first-half. We should be winning the game at half-time.
"In the second-half, we reshaped the team. The injury to Carney Chukwuemeka, we didn't find a way from the beginning. Then when we started to find a way to play, we then conceded another goal. Then we started to take different decisions, trying to find the right timing in offensive situations. Yes, disappointed but this is a process and we need to keep working."