West Ham boss Manuel Pellegrini felt they took too long to get into the game after Monday night's 2-0 defeat at Chelsea.
Eden Hazard scored both goals for Chelsea's victory over West Ham.
“We improved a lot in the second half," he explained, “We had opportunities, and we could have drawn the game but finally they scored the second goal.
“I think the difference was in the first 45 minutes, that we didn't start the game with the pace that you need to play [against Chelsea].
“When a player with the quality of Hazard, you know he can make different things. Going between four players is not easy, so maybe we could have been more aggressive. That was our attitude in the first 45 minutes, in the way we defended that goal and the way we played.
“After that, I think we changed a lot of things, in the pace we played and the part of the pitch we played in too. We played forward and not so close to our box, and we had the chances to draw."