Maurizio Sarri praised his players after their 3-2 victory over Arsenal but admitted their defensive shortcomings had been exposed.
Marcos Alonso scored a late winner for Chelsea after Arsenal had come back from two down.
The Blues have won both their first two Premier League games under Sarri but the head coach believes failing to press in their opponents’ half of the pitch often leads to them looking vulnerable at the back.
Sarri explained: “I think we have to work to improve in the defensive phase – and we are not only talking about defenders. The defence is all the players.
“If we press very high we are able to do well but at other moments, when we are not able to press, we are in trouble. I think we have to work and we have to improve.
“We need to press and press and press in the other half, otherwise we are in trouble.”
Early goals from Pedro and Alvaro Morata put Chelsea in control but Arsenal scored twice in the space of four minutes before the interval and missed three other glorious chances to score.
“I think we did very well for 75 minutes. For 15 minutes of the first half it was horrible,” Sarri admitted.
“The players were very good in the second half. They had to work hard to answer what had happened in the final part of the first half.”