Cape Town - Slaven Bilic acknowledged that mistakes from West Ham led to both Chelsea goals in their 2-1 loss at the London Stadium on Monday night.
Eden Hazard had given the Blues a 25th minute lead ahead of a second five minutes after the break from Diego Costa, while Manuel Lanzini netted a consolation goal in injury time at the end of the game.
The Hammers were guilty of conceding possession far too early for the opener, with Bilic explaining that you can't expect to beat the Blues when you gift them goals.
He told the club's official website: "To make such a mistake that led to their first goal when we had our centre-backs in their box – we should have put the ball back in the box – but we didn’t and they scored the counter-attack.
“Their second goal was also a cheap one from our side. So basically, it’s very simple. If you want to beat Chelsea, then you can’t make those kind of mistakes. You have very little chance if you do.
“The first was a set piece for us and we had enough players back. We had a chance to put in the second ball in a good position but we didn’t, Mark wanted to play with the best intentions, but you expect your players to run back with more reason in this situation.
“Chelsea players are all in and around the box as well but they got the ball in space where we can’t afford to give it, especially against them because their pace in the transition is scary.”
Bilic felt his side had started the match brightly.
He added: "We played well in the first half – we started really, really well. We were on top.
“Then we made that cheap mistake in a place that against them you can’t."
Up next for West Ham is a trip to Bournemouth next week, with Bilic concluding: "We have a game against Bournemouth now and it’s a very big game for us. We have to prepare ourselves and try to get back to winning.”