The Blues missed the chance to move up to third in the Premier League after they were beaten by their London rivals by a late Andriy Yarmolenko goal and their manager believes his team's mistakes are holding them back.
Speaking after the match, he told the BBC: "It happens, it is the Premier League and if you make mistakes like we did, we dominated the game in terms of possession, but make mistakes and teams will hurt you.
"I'm not happy with any of the goals. You don't get given victories for scoring two goals, you have to be better than that."
'There were moments they counter-attacked, which we knew they would. There were details in the game which we knew but we lost because we didn't get them right. "
Lampard admits that the defeat showed Chelsea's limitations and why they are scrapping for the Champions League places.
The 42-year-old coach: "It is why we are fighting for top four not one or two, because we don't get things right as much as the big boys do. I am not happy with tonight but at the same time we are two points ahead of Manchester United, who have been going great for some time."
The Chelsea legend also challenged his team to show more consistency and to defend better.
Lampard said: "If you don't get details right in big games, you're going to drop points. I think at times we have played really well this season. As a group we need to find more consistency.
"We have to defend the moment better. Against West Ham you have to make recovery runs. That is the bit we got wrong."