Tottenham Hotspur head coach Mauricio Pochettino says his side should have done better in the early stages of the game against West United.
Spurs lost an opportunity to go top of the Premier League as they suffered a 1-0 away defeat against the Hammers.
And the 44-year-old says the focus will now be shifted to Saturday's home game against Arsenal.
"I think that we didn't start the game in a good way," Pochettino told BBC Sport.
"We made some mistakes and the team didn't feel free to play the way they play. West Ham is a strong, physical team which made it difficult and the conditions favoured them because the pitch wasn't good.
"We need to be positive and it is important to be ready for Saturday. When you lose you can blame that the players are tired or whatever but the reality is that it was just a bad night for us to play the way we play tonight.
"The players are sad and it is true that we are very motivated and excited to stay towards the top of the table. I feel proud of them as the effort was fantastic."